81.	This question is about the compounds of Group 6 elements with hydrogen.
	The table below shows some of the boiling points and molar masses of these hydrides.
Hydride	Boiling point /K	Mass of 1 mole /g	
Water, H2O	––	18	
Hydrogen sulphide, H2S	212	34	
Hydrogen selenide, H2Se	232	––	
Hydrogen telluride, H2Te	271	130	
(a)	What is the mass of one mole of hydrogen selenide, H2Se?
Use the Periodic Table as a source of data.

(1)

(b)	(i)	Plot a graph of the boiling points of the three hydrides H2S, H2Se, and H2Te against their molar masses.

(2)
(ii)	Why do the boiling points of these hydrides increase as the molar mass increases?
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)

(c)	(i)	Use your graph to predict the boiling point of water if it were to follow the pattern of the other three hydrides.
..........................................................................................................................
(1)
(ii)	What causes the boiling point of water to be 373 K, rather than your answer in (i)?
..........................................................................................................................
..........................................................................................................................
(1)
(iii)	Explain why this arises in water and not in the other hydrides.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(1)
(iv)	Give the names of TWO other hydrides which, like water, have boiling points higher than you would expect.
..........................................................................................................................
..........................................................................................................................
(2)
(d)	Give TWO properties of water, other than high melting and boiling points, which are brought about by the strong intermolecular forces between water molecules.
..........................................................................................................................
..........................................................................................................................
(2)
(Total 12 marks)

82.	Read the passage below on CYANIDE – A TOXIC PARTNERSHIP straight through, and then more carefully in order to answer the following questions.
	CYANIDE – A TOXIC PARTNERSHIP
	Hydrogen cyanide was discovered by the Swedish apothecary and chemist Carl Wilhelm Scheele in 1782. He isolated hydrogen cyanide while working on the destructive distillation of the pigment Prussian Blue. By distilling the fumes formed and heating the product, he obtained a small quantity of aqueous acid which he named prussic acid. It had, he reported ‘. . . a taste which almost borders slightly on sweet and is somewhat heating in the mouth’. Surprisingly, having tasted his new compound, Scheele was to survive for another three years. Although his death has been attributed to him inhaling HCN vapour when a flask broke, a more satisfactory historical account suggests that he actually died from a combination of disorders, including rheumatism and gout.

	In the early 19th century the study of prussic acid was taken up by Gay-Lussac, who in the course of his work prepared pure HCN, and also the gas cyanogen, (CN)2.
	Hydrogen cyanide is a colourless, low viscosity liquid with the smell of bitter almonds, though in fact not everyone can smell it. It is a weak acid and is found in nature, for example, during photosynthesis and is produced when a number of synthetic polymers, such as polyurethane furniture foams, burn.
	Today, hydrogen cyanide is prepared by reacting ammonia with hydrocarbons by either the Andrussov process or the Degussa process. In the first process, the mixture is oxygenated, and passed over a precious metal catalyst at slightly elevated pressure and high temperatures.
CH4(g) + NH3(g) + 1½O2(g)  HCN(g) + 3H2O(g)
	In the alternative process, developed by the company Degussa, a simpler catalyst system is used and it operates in the absence of oxygen.
CH4 + NH3  HCN + 3H2
	Both processes employ rapid flow rates and each gives yields approaching 90%.
	Hydrogen cyanide polymerises to give a black solid. To prevent this happening, small quantities of stabilisers, typically strong acids such as sulphuric or phosphoric acid, are added. The major use of hydrogen cyanide is in the synthesis of other compounds, such as the monomer methyl methacrylate (used to make Perspex), as well as pharmaceuticals and speciality chemicals.

	From 1887, sodium cyanide was used for extracting gold and silver from their ores. Gold occurs in its ores in a chemically free state as finely divided metallic particles. Extraction by the cyanide process involved crushing the gold-bearing rock, followed by treatment with a dilute solution of sodium cyanide plus lime to control the pH. The mixture was aerated and reacted according to the following equation
4Au + 8NaCN + O2 + 2H2O ® 4Na[Au(CN)2] + 4NaOH

	The resulting gold complex was then treated with zinc dust to precipitate the product, after which the gold was liberated by electrolytic refining.
Potassium cyanide is used in electroplating and also in the manufacture of dyestuffs. Typically, plating is carried out by depositing silver onto the object by making it the cathode in a bath consisting of an aqueous solution of both silver and potassium cyanides.
	A surprising application for a cyanide complex is sodium hexacyanoferrate(II), Na4[Fe(CN)6], in table salt to prevent caking. Manufacturers of table salt seem coy about admitting to this use, at least to the consumer, and bland terms appear in the list of ingredients, such as ‘anti-caking agent’. Whatever it is called, this particular cyanide complex acts by absorbing water and forming hydrates. This counteracts the natural tendency of sodium chloride to take up water and thus to form solid lumps. Like all cyanides, this substance is toxic, but the levels added to table salt are such that the daily dose is well below the recommended maximum of 0.025 mg kg–1 body weight.
(612 words)
	Adapted from ‘Cyanide – a toxic partnership’, by John W. Nicholson, Education in Chemistry, March 1996.
(a)	(i)	Draw a ‘dot-and-cross’ diagram for hydrogen cyanide, HCN.
(1)
(ii)	Predict the bond angle in HCN.
(1)
(b)	Give ONE reason for and ONE reason against the use of a slightly elevated pressure in the Andrussov process for the preparation of hydrogen cyanide.
(2)
(c)	Draw the formula for the repeat unit of Perspex.
(1)
(d)	The reaction between gold and sodium cyanide to form a gold complex is a redox reaction.
(i)	Give the name of the element which is oxidised and show its change in oxidation number.
(1)
(ii)	Give the name of the element which is reduced and show its change in oxidation number.
(1)

(e)	Describe in no more than 100 words
·	the two methods currently used to make hydrogen cyanide
·	a use of hydrogen cyanide
·	a use of another cyanide.
	You are not asked to summarise the whole passage nor to use chemical formulae or equations in your answer.
	At the end of your summary, state the number of words you have used.
(8)
	Credit will be given for answers written in good English, using complete sentences and with the correct use of technical words. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations and hyphenated words. Any title you give to your passage does not count in your word total.
	There are penalties for the use of words in excess of 100.

83.	Iodine is obtained from three sources: sea water, seaweed and nitrate ores.
(a)	(i)	Sea water containing iodide ions is concentrated, and then chlorine gas is bubbled through the solution.
	Write the balanced ionic equation, including state symbols, for the reaction between chlorine gas and iodide ions.

(2)
(ii)	What is the final colour of the solution at the end of this reaction?
.............................................................................................................................
(1)
(b)	In nitrate ores, iodine occurs in the form of iodate ions, .
	The first step of the process to extract iodine involves reaction of iodate ions with sulphur dioxide gas to form iodide ions and sulphate ions, .
(i)	State the oxidation number of iodine in
iodide ions, I- ....................................................................................................
iodate ions,  ................................................................................................
(1)

(ii)	State the oxidation number of sulphur in
sulphur dioxide, SO2 ........................................................................................
sulphate ions,  ..........................................................................................
(1)
(iii)	Balance the ionic equation for the reaction between iodate ions and sulphur dioxide gas to produce iodide ions and sulphate ions.
(aq) + .......SO2(g) + .......H2O(l) ® I-(aq) + .......(aq) + .......H+(aq)
(2)
(c)	(i)	The next step is to add a small quantity of a solution containing iodate ions. These react with the iodide ions present to form an iodine solution.
	Iodine can be extracted from this solution by the addition of a hydrocarbon solvent and separation of the hydrocarbon solution using a separating funnel.
	Draw a diagram of a separating funnel and its contents. Indicate which is the hydrocarbon layer and state its colour. [Density of the hydrocarbon is 0.660 g cm-3]

	Colour of hydrocarbon layer .............................................................................
(3)
(ii)	How might solid iodine be obtained from the hydrocarbon layer?
............................................................................................................................
(1)
(Total 11 marks)

84.	The industrial processes involved in the production of poly(chloroethene) are summarised in the flow chart:
ethane ® ethene ® 1,2-dichloroethane ® chloroethene ® poly(chloroethene)
(a)	(i)	Ethane is converted to ethene by dehydrogenation.
	Write a balanced equation, including state symbols, for this equilibrium reaction.

(1)
(ii)	Explain why conditions of high pressure are less favourable for ethene production.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(b)	Draw a labelled diagram of an ethene molecule, showing the electron density distribution in the s and p bonds between the carbon atoms.

(2)
(c)	Give a chemical test which would distinguish between ethane and ethene.
	State the result of your test with ethene.
Test ..............................................................................................................................
Result ...........................................................................................................................
(2)
(d)	1,2-dichloroethane is formed from ethene by reaction with chlorine. 
	State the type and mechanism of this reaction.
Type ...................................................................................................................................
Mechanism .........................................................................................................................
(2)

(e)	(i)	Suggest a reagent and TWO conditions for making chloroethene from
1,2-dichloroethane in the laboratory.
Reagent .......................................................................................................................
Conditions ...................................................................................................................
(2)
(ii)	Name both types of intermolecular force between chloroethene molecules.
.............................................................................................................................
.............................................................................................................................
(1)
(f)	(i)	Write a balanced equation for the formation of poly(chloroethene) from chloroethene.

(2)
(ii)	Poly(chloroethene) is also known by the name polyvinylchloride, PVC.
	Give TWO common uses of poly(chloroethene).
.............................................................................................................................
.............................................................................................................................
(2)
(Total 16 marks)

85.	Phosphine, PH3, is a hydride of the Group 5 element, phosphorus.
(a)	(i)	Draw a ‘dot-and-cross’ diagram of a phosphine molecule. You should include only outer shell electrons.

(1)

(ii)	Draw the shape you would expect for the phosphine molecule, suggesting a value for the HPH bond angle.

HPH bond angle .......................................................................................................
(2)
(iii)	Explain the shape of the phosphine molecule you have given in your answer in (ii).
	Justify your value for the HPH bond angle.
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
(2)
(b)	(i)	Write a balanced equation, including state symbols, for the atomisation of phosphine gas.
.............................................................................................................................
(1)
(ii)	Use your answer to (i) and the data below to calculate the standard enthalpy change of atomisation of phosphine at 298 K. Include a sign and units in your answer.
ΔHοf[PH3(g)]	=	+	5.4 kJ mol-1
ΔHοat[½H2(g)]	=	+	218.0 kJ mol-1
ΔHοat[P(s)]	=	+	314.6 kJ mol-1

(3)

(iii)	Calculate a value for the bond energy of the bond between phosphorus and hydrogen, using your answer to (ii).

(1)
(Total 10 marks)

86.	This question is about phosphine, PH3, and ammonia, NH3.
(a)	Which compound has the stronger van der Waals forces?
	Justify your answer.
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)	(i)	The boiling points of ammonia and phosphine are:
	Ammonia	240 K
Phosphine	185 K 
	Name the intermolecular force responsible for the higher boiling point of ammonia.
...........................................................................................................................
(1)
(ii)	Use displayed formulae to show this intermolecular bond between two ammonia molecules.
	Clearly mark and label the bond angle between the molecules.

(2)

(c)	Indicate the solubilities of silver chloride, silver bromide and silver iodide in dilute and concentrated ammonia solution by completing the table. Write the word soluble or insoluble as appropriate.
	Silver chloride	Silver bromide	Silver iodide	
Dilute ammonia solution				
Concentrated ammonia solution				
(2)
(d)	Ammonia can also be used to test for hydrogen chloride gas.
(i)	What would you see if a glass rod, dipped in ammonia solution, is placed in hydrogen chloride gas?
............................................................................................................................
(1)
(ii)	Write a balanced equation for this reaction.

(1)
(Total 8 marks)

87.	Read the passage below on THE DANGERS OF EXPOSURE TO THE SUN AND HOW TO AVOID THEM straight through, and then read it again more carefully, in order to answer the following questions.
	THE DANGERS OF EXPOSURE TO THE SUN AND HOW TO AVOID THEM
	During the latter part of the twentieth century a suntan became associated with fitness, youth and health. Increasing leisure time and cheap travel have helped certain populations to increase their lifetime ultraviolet radiation (UVR) exposure way beyond previous generations. Unfortunately this level of UVR exposure has increased the risk of damage to the skin caused by sunlight, called cutaneous photodamage. This photodamage has two potentially undesirable effects – premature ageing of the skin, called photoaging, and skin cancer.
	When skin is exposed to ultraviolet radiation a proportion of the energy of the radiation is absorbed. Initially electrons in molecules in the skin are promoted to higher energy levels, producing electronically excited molecules. These electronically excited molecules may react in several ways. They might simply break up heterolytically to produce fragment ions which react to produce toxic photoproducts. They may form highly reactive free radicals, or powerful oxidising agents by reaction with oxygen, which damage cells or other biologically important molecules. Finally, they may directly interact with cells in a damaging way.
	There are three ways of reducing the risk from UVR exposure. These are directly limiting sun exposure by avoiding going out in the sun, the use of appropriate clothing and the careful use of sunscreen products.
	Directly limiting sun exposure is effective. However, it is socially unacceptable and, with a desirable increase in outdoor activities like jogging, it is impractical.
	Clothing which is made of opaque fabric is effective. It is important that the fabric is not flimsy or ‘see-through’. It should also be noted that many fabrics lose as much as 70% of their sun protection factor when wet. Broad-brimmed hats can reduce head and neck exposure significantly, but will still allow about 30% of damaging radiation exposure from reflected light, particularly when near sand or water.
	There are two main types of sunscreen preparations, those that reflect the sun’s rays, and those that filter out the harmful UVR.
	Historically, the first reflective preparation was issued to soldiers during the Second World War. Known as ‘Red Vet Pet’, it was a suspension of iron(III) oxide in petroleum jelly. It was extremely effective but was thick, greasy and gave a bizarre appearance. Nowadays similar effective preparations, which reflect harmful UVR, use zinc oxide or titanium dioxide.  The only problem with these is one of cosmetic acceptability. As well as reflecting UVR, they tend to reflect visible light giving the user the appearance of a circus clown. Recently this problem has been overcome by using a very fine particle size of titanium dioxide which limits the reflection of visible wavelengths. This type of sunscreen has the major advantage of reflecting all wavelengths of ultraviolet radiation.
	A wide variety of chemicals are used in filter preparations. These include esters of 4-aminobenzoic acid, esters of cinnamic acid, benzophenones, salicylates, and anthranilates. These usually act by absorbing harmful ultraviolet radiations. The disadvantage is that these chemicals only absorb over a small range of ultraviolet frequencies, so some harmful radiations will still reach the skin. The key is to check on the package of sunscreen that it is effective against both UVA and UVB, the two ranges of UVR frequencies which are known to be harmful.
(533 words)
	Adapted from ‘The benefits of lifetime photoprotection’ by J Gray and J L M Hawk published by the Royal Society of Medicine Press, and ‘Sun damaged skin’ by Ronald Marks published by Dunitz.
(a)	What are the TWO reasons for increased exposure to the sun nowadays?
(1)
(b)	What are the TWO undesirable effects of exposure to ultraviolet radiation?
(2)
(c)	What is meant by the following terms:
(i)	heterolytically
(ii)	free radical
(iii)	oxidising agent?
(3)
(d)	Write a summary, in no more than 100 words, describing the methods for avoiding exposure to ultraviolet radiation and how effective they are.
(9)

	You are NOT asked to summarise the whole passage, or to include equations in your summary.
	At the end of your summary state the number of words you have used.
	Credit will be given for answers written in good English, using complete sentences and using technical words correctly and chemical names rather than formulae. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations, units and hyphenated words. Any title you give your passage does not count in your word total.
	There are penalties for the use of words in excess of 100.

88.	The table below shows some data for four organic compounds.
	Butane	Propan-1-ol	Propan-2-ol	Propanone	
Structural
formula	CH3CH2CH2CH3	CH3CH2CH2OH	CH3CH(OH)CH3	CH3COCH3	
Number of
electrons per
molecule	34	34	34	32	
Boiling
point/°C	–0.5	97.2	82.4	?	
(a)	The molecules of each compound contain a similar number of electrons. 
What type of intermolecular forces are likely to be similar in strength?
......................................................................................................................................
(1)
(b)	Explain why propan-1-ol boils at a higher temperature than
(i)	butane
...............................................................................................................................
...............................................................................................................................
(1)
(ii)	propan-2-ol.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(2)

(c)	(i)	Draw the displayed formula and a ‘dot and cross’ diagram for propanone, showing outer shell electrons only.

(2)
(ii)	Give the values for the HCH and the CCO bond angles in propanone.
HCH bond angle ..................................
CCO bond angle ...................................
(2)
(iii)	What type of intermolecular bonding is present in propanone but not in butane?
...............................................................................................................................
(1)
(iv)	Use the data in the table above to estimate the boiling point of propanone.
...............................................................................................................................
(1)
(d)	Propanone dissolves in water whereas butane does not. Suggest a reason for this.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(1)
(Total 11 marks)

89.	(a)	Hydrogen chloride gas can be prepared by the reaction of concentrated sulphuric acid with solid potassium chloride.
(i)	Write a balanced equation for this reaction. State symbols are not required.

(1)

(ii)	Draw a labelled diagram of apparatus which could be used to prepare and collect samples of this gas.

(2)
(b)	(i)	State what you would see if hydrogen chloride gas is allowed to come into contact with ammonia gas.
..........................................................................................................................
(1)
(ii)	Write an equation for this reaction, including state symbols.

(1)
(iii)	Name the product of this reaction. ...................................................................
(1)
(c)	Hydrochloric acid, formed when hydrogen chloride is dissolved in water, can be converted to chlorine using an aqueous solution of hydrogen peroxide:
2HCl(aq) + H2O2(aq) ® Cl2(g) + 2H2O(l)
(i)	Give the oxidation numbers of
chlorine in HCl ..........	chlorine in Cl2 ..........
oxygen in H2O2 ..........	oxygen in H2O ..........
(2)
(ii)	Name the reducing agent in this reaction.
...............................................................................................................................
(1)

(iii)	Explain why the oxidation numbers you have given in (i) are consistent with the fact that two moles of hydrochloric acid react with one mole of hydrogen peroxide.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(1)
(d)	Chlorine can be converted to the gas chlorine(I) oxide, Cl2O.
	The standard molar enthalpy change of formation of chlorine(I) oxide and the standard molar enthalpy changes of atomisation of chlorine and oxygen are given below:
ΔHfο [Cl2O(g)]	=	+ 80.3 kJ mol–1
ΔHatο [½Cl2(g)]	=	+121.7 kJ mol–1
ΔHatο [½O2(g)]	=	+249.2 kJ mol–1
	A partially completed Hess cycle involving chlorine(I) oxide is shown below:

(i)	Insert the appropriate formulae, showing the correct quantities of each element, into the box above. Include state symbols in your answer.
(1)
(ii)	Insert arrows between the boxes, writing the correct numerical data alongside the appropriate arrows.
(1)

(iii)	Use the cycle to calculate ΔHatο  [Cl2O(g)].

(1)
(iv)	Calculate the Cl—O bond energy in chlorine(I) oxide.

(1)
(Total 14 marks)

90.	Some reactions of 2-bromobutane are shown in the scheme below:

(a)	(i)	Name the reagent R and give the conditions under which Reaction 1 takes place.
Name of reagent R ...........................................................................................
Conditions ........................................................................................................
(2)
(ii)	Give the type and mechanism of Reaction 1.
Type .................................................................................................................
Mechanism ......................................................................................................
(2)
(b)	(i)	Give the structural formula of the organic compound S formed in Reaction 2.

(1)
(ii)	A precipitate would also be formed during this reaction. State its colour. Write an ionic equation, with state symbols, for its formation. Omit any spectator ions.
Colour of precipitate ..............................................................................................
Ionic equation

(2)
(iii)	A similar experiment was carried out with 2-chlorobutane, rather than 2-bromobutane.
	What difference would there be in the rate of formation of a precipitate?
	Explain your answer.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(2)
(c)	(i)	In Reaction 3, give the name of a suitable reagent T and describe the reaction conditions used.
Name of reagent T .................................................................................................
Conditions ..............................................................................................................
(2)
(ii)	Draw displayed formulae of the two geometric isomers of CH3CH==CHCH3.

(1)

(iii)	Explain why CH2==CHCH2CH3 does not possess geometric isomers.
....................................................................................................................
...............................................................................................................................
...............................................................................................................................
(1)
(Total 13 marks)

91.	But-1-ene, CH2==CHCH2CH3, can be converted into a polymer.
(a)	Draw the structure of part of the polymer, showing TWO repeating units.

(2)
(b)	The polymerisation of CH2==CHCH2CH3 is exothermic and involves the use of a catalyst. The diagram below shows the energy profile for this polymerisation using a catalyst.

	Indicate on the profile the activation energy for the catalysed process.
	Add another energy profile to the diagram for the polymerisation where a catalyst is not used.
(3)

(c)	Explain, in terms of activation energy and the collision theory, why the rate of polymerisation is greater when
(i)	a catalyst is used
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(1)
(ii)	heat energy is provided to start the process.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(1)
(Total 7 marks)

92.	Read the passage below on CHEMISTRY THAT WON’T LET YOU DOWN straight through, and then more carefully, in order to answer the following questions.
	CHEMISTRY THAT WON’T LET YOU DOWN
	The current deodorant, antiperspirant and body spray market in the UK is estimated to be worth £447 million. This represents approximately 30% of the toiletries sector which makes up almost a third of the entire cosmetics market. So what is the story behind antiperspirants and deodorants?
	Sweating plays a vital role in controlling the body’s temperature. The evaporation of a watery fluid from sweat glands on the surface of skin has a cooling effect. During sweating, pheromones, chemicals that identify us through odour, are secreted. Sweat glands, of which there are two types, occur over most of the body surface. They are most abundant in the armpits, the groin, on the soles of the feet, the palms of the hands and the forehead. Eccrine glands, of which there are about two to four million over 99% of the body, are triggered by emotional, thermal and sensory stimuli. The sweat which they produce is virtually odourless and is essentially a dilute aqueous solution containing mainly sodium chloride and urea, and also other metabolic waste products, such as the lactates produced in muscles. Emotional stimuli also trigger the aprocrine glands, which are found only in the armpit and groin. Aprocrine glands produce small amounts of secretions rich in proteins and lipids, together with cholesterol and steroids. These fatty compounds are broken down by bacteria on the skin surface, mostly to low carbon chain (C4–C10) fatty acids, RCOOH, such as 3-methylhexanoic acid, which we recognise as body odour (BO).

	Antiperspirants and deodorants share many of the same ingredients. However, each has its own distinct role and contains different active compounds.
	Deodorants act solely to reduce BO by killing the odour-causing bacteria. The first deodorant, marketed in the US in 1888, was “Mum”, a zinc oxide based cream. Chemists soon discovered that other zinc-based compounds such as zinc peroxide were anti-bacterials and therefore also had deodorant potential. In the early 1960s Gillette introduced an aerosol deodorant, “Right Guard”, that contained essentially two antibacterial agents, zinc phenolsulphonate and hexachlorophene. While zinc phenolsulphonate remains one of the few zinc salts clinically accepted in deodorants, hexachlorophene was banned in the mid-1970s because of its toxicity. In today’s deodorants, ethanol is the principal antibacterial agent. Further antibacterial activity is derived from some of the added perfume oils, for example, the essential oils of sage and lemon, and additional antibacterial agents such as triclosan.
	In contrast to deodorants, antiperspirants have a dual action, reducing both odour and wetness. Antiperspirants usually contain aluminium salts, which physically block the eccrine sweat glands. Aluminium salts are also antibacterial agents and therefore have a deodorising effect.
	“Everyday”, launched in 1902, was the first branded antiperspirant. It was an aqueous solution of aluminium chloride which was dabbed onto the armpits with cotton wool. Unfortunately with a pH of about 2 the “Everyday” solution was so acidic that it irritated the skin and rotted clothes. Early attempts in 1921 to counteract the corrosive nature of this solution used borax and alum, but eventually urea became the agent of choice. These products were cold and wet to apply and slow drying. It was not until John H. Wallace, a Princeton chemist working for Carter Medicine, developed “Arrid Cream” in 1934, which used the less corrosive aluminium sulphate, that antiperspirant products began to have as much appeal as deodorants like “Mum”.
	In 1947, two chemists, T. Gorett and M. G. deNavarre, used the more basic aluminium salts, known as aluminium chlorohydrates (ACH) with the general formula Al2(OH)mCln, where m + n = 6, in antiperspirant formulations, with more success. These are still used extensively in antiperspirants today.
	Deodorants and antiperspirants are sold in three different formulations: solutions, suspensions and emulsions. These are applied in several different ways: pump sprays developed from World War II insecticide sprays, roll-ons, an idea inspired by Ladislas and Georg Biro’s ballpoint pen, as well as sticks, aerosols and gels.
	In the personal hygiene market cosmetic companies are continually trying to win over customers. Formulation chemists will continue to develop products that provide optimum performance, effective application and pleasant use. 
[635 words]
	Adapted from “Chemistry That Won’t Let You Down” by James Berressem, Education in Chemistry, July 2002.
(a)	What does sweat, produced by the eccrine glands, contain?
(1)
(b)	State THREE factors which stimulate the creation of sweat.
(1)
(c)	Suggest the structural formula for 3-methylhexanoic acid.
(2)

(d)	What was the main problem associated with the use of the earliest antiperspirants?
(1)
(e)	Write the formula of the “ACH” antiperspirant in which m = 2.
(1)
(f)	Suggest ONE advantage of applying an antiperspirant as a “roll-on”, as opposed to using it in an aerosol. 
(1)
(g)	Write a summary in no more than 100 words, in which you
·	explain the distinction between deodorants and antiperspirants
·	describe their composition nowadays and how they work
·	give the different formulations and ways in which they can be applied to the skin.
(8)
	You are NOT asked to summarise the whole passage, nor to include equations in your summary. At the end of your summary state the number of words you have used.
	Credit will be given for answers written in good English, using complete sentences and with the correct use of technical words. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations, units and hyphenated words. Any title you give your passage does not count in your word total.
	There are penalties for the use of words in excess of 100.

93.	(a)	A few crystals of potassium iodide were put into a test tube with a similar quantity of phosphoric acid, H3PO4. The mixture was warmed. Misty white fumes were seen at the mouth of the test tube.
(i)	Give the name or formula of the misty white fumes which formed in this reaction.
................................................................................................................................
(1)
(ii)	Write a balanced equation for the reaction. State symbols are not required.
H3PO4 +         KI →	+
(2)
(iii)	A sample of the misty white fumes was collected and dissolved in water.
	What reagent would be used to confirm the identity of the halide ion present in the solution? State what you would expect to see when it is used.
Reagent ..................................................................................................................
Observation ............................................................................................................
(2)

(b)	If potassium iodide crystals are reacted with concentrated sulphuric acid, a complicated reaction occurs in which a mixture of gases is produced.
(i)	What would you see, other than misty white fumes, when this reaction occurs? Give ONE observation.
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................................................................................................................................
(1)
(ii)	One of the gases in the mixture is hydrogen sulphide, H2S. It can be identified by holding a piece of filter paper soaked in a solution of lead nitrate, Pb(NO3)2, or lead ethanoate, (CH3CO2)2Pb, in the gas.
	What would be observed if hydrogen sulphide is present?
................................................................................................................................
................................................................................................................................
(1)
(iii)	Suggest the name of the lead compound which forms in this reaction, using Stock notation.
........................................................................
(1)
(iv)	The equation below shows how hydrogen sulphide could be produced from sulphuric acid in a redox reaction.
	9H2SO4 + 8KI → H2S + 8KHSO4 + 4H2O + 4I2
	Which element is oxidised in the reaction and which is reduced? Justify your answer by calculating oxidation numbers.
	Element oxidised .................................
	Initial oxidation number .......................  Final oxidation number ......................

	Element reduced ..................................
	Initial oxidation number .......................  Final oxidation number ......................
(3)

(c)	An experiment was carried out to measure the purity of a sample of potassium iodide.
	1.75 g of impure potassium iodide was dissolved in water, and excess chlorine was passed through the solution. The following reaction occurred.
Cl2(g) + 2KI(aq) → I2(aq) + 2KCl(aq)
	The solution was warmed to drive off the excess chlorine and was then made up to 250 cm3 in a volumetric flask. A titration was used to measure the concentration of iodine in the solution.
(i)	What solution could be used in a titration to measure the concentration of iodine?
................................................................................................................................
(1)
(ii)	Name a suitable indicator and state the colour change at the end-point of this titration.
	Indicator .................................................................................................................
	Colour change from ......................................     to ...............................................
(2)
(iii)	A titration showed that the solution contained 4.8 × 10–4 moles of iodine, I2, in a 25 cm3 sample. Calculate the number of moles of potassium iodide, KI, which were in the original impure sample.

(1)
(iv)	Calculate the percentage purity of the potassium iodide.
Use the Periodic Table as a source of data.

(2)
(Total 17 marks)

94.	This question is about the chemistry of methanol, CH3OH.
(a)	(i)	Draw a ‘dot and cross’ diagram for methanol, showing outer shell electrons only.

(1)
(ii)	Textbooks show the displayed formula of methanol as follows

	However, this is not a true representation of the shape of the molecule.
Explain why the shape of methanol is not as shown above.
Label the correct value of ONE bond angle on the displayed formula.
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................................................................................................................................
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(2)
(b)	When methanol burns in a poor supply of air, one of the products is carbon monoxide.
A ‘dot and cross’ diagram of carbon monoxide is shown below.

(i)	Draw the displayed formula for carbon monoxide. Show the TWO types of bond which are present.

(1)

(ii)	The length of the bond between carbon and oxygen in methanol is 0.143 nm. Would you expect the length of the bond between carbon and oxygen in carbon monoxide to be longer, the same or shorter than this? Explain your answer.
................................................................................................................................
................................................................................................................................
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(2)
(c)	The energy of the bond between carbon and oxygen in methanol (the C—O bond) can be calculated from data on enthalpy changes of atomisation.
(i)	Write an equation, including state symbols, for the atomisation of one mole of methanol vapour.

(1)
(ii)	Use the data below to calculate the energy of the C—O bond in methanol.
	standard enthalpy change of atomisation of methanol vapour, ∆Hοat = +2039 kJ mol–1
energy of C—H bond, E(C—H) = +413 kJ mol–1
energy of O—H bond, E(O—H) = +464 kJ mol–1

(2)

(iii)	Complete a balanced Hess cycle which you can use to calculate the standard enthalpy change of formation of methanol vapour, DHοf.
	You should use the value of the standard enthalpy change of atomisation of methanol vapour, DHοat, given in (ii) and the data on enthalpy changes given below. Write the correct numerical data beside the arrows in the cycle.
	Equation		Enthalpy change of atomization
		/kJ mol–1
	C(graphite) ® C(g)	+716.7
	½ O2(g) ® O(g)	+249.2
	½ H2(g) ® H(g)	+218.0

	Use your cycle to calculate the value of DHοf for methanol vapour.

(3)

(iv)	Methanol is a liquid at room temperature. Would you expect the standard enthalpy change of formation of liquid methanol to be more or less negative than the value you calculated in (iii)? Justify your answer.
................................................................................................................................
................................................................................................................................
(1)
(v)	Methanol is a liquid at room temperature although alkanes with similar molecular mass are gases.
	Draw a diagram to show a bond between two methanol molecules that causes it to be a liquid at room temperature.
	Give the value of this bond angle on your diagram.

(2)
(d)	Methanol can be manufactured in the following reaction.
CO(g) + 2H2(g)  CH3OH(g)	∆Hο = –93.3 kJ mol–1
	Decide whether a high or low temperature and a high or low pressure would give the greater proportion of methanol at equilibrium. Justify your choice in each case.
Temperature ..................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
Pressure .........................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
(2)
(Total 17 marks)

95.	(a)	The table below gives the boiling points of three organic compounds.
Compound	Boiling point
/K	
chloroethane	285	
1-chloropropane	320	
2-chloropropane	309	
(i)	Explain why 1-chloropropane has a higher boiling point than chloroethane.
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(2)
(ii)	Explain why 1-chloropropane has a higher boiling point than its isomer, 2-chloropropane.
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(1)
(b)	Both chloroethane and iodoethane react with aqueous potassium hydroxide solution to form ethanol. The hydroxide ions act as nucleophiles.
(i)	What is a nucleophile?
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................................................................................................................................
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(1)
(ii)	Explain why iodoethane reacts faster than chloroethane with aqueous potassium hydroxide, under the same conditions.
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(1)

(c)	(i)	Under what conditions does chloroethane react with potassium hydroxide to form ethene rather than ethanol?
...............................................................................................................................
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(1)
(ii)	Name the type of reaction in which ethene is formed from chloroethane.
...............................................................................................................................
(1)
(d)	Ethanol can be produced from ethene in two stages. In the first stage ethene is reacted with concentrated sulphuric acid in an addition reaction.
(i)	Complete the equation to show the product of the first stage in the process.
	
(1)
(ii)	What type of addition reaction is occurring?
...............................................................................................................................
(1)
(iii)	How is the product of this reaction converted to ethanol?
...............................................................................................................................
(1)
(e)	In industry, ethanol is usually manufactured from ethene, rather than by reacting chloroethane with aqueous potassium hydroxide. Suggest a reason for this.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(1)
(Total 11 marks)

96.	Read the passage below straight through and then more carefully.
	A RADICAL ALTERNATIVE TO IONS
	Reactions involving free radicals were once believed to be unselective and low-yielding and therefore of little use to chemists. There is no doubt that free radicals get a pretty bad press. Radicals generated from chlorofluorocarbons are known to destroy the Earth’s ozone layer, while radicals made in the body are believed to contribute to many diseases, including heart disease and stroke. Even the rancidity of margarine is blamed on undesirable radical reactions. In these instances, it is easy to see why the formation of radicals should be avoided, though this is not always the case. There are many useful and efficient radical reactions currently being developed by organic chemists.
	The most important method for making polymers involves radicals. In industry, radical chain reactions are used to make a number of useful polymers, including poly(chloroethene), poly(phenylethene) and poly(ethene). Such polymers have numerous uses, for example in electrical insulation, grocery bags, raincoats, swimming pool liners, tubing and foam packaging. Radical polymerisation is used to prepare poly(tetrafluoroethene), (PTFE or Teflon), which is used to coat non-stick pans. Polymerisation reactions involving radicals can produce polymers of varying chain length and degrees of chain branching.
	Uses of radicals in organic synthesis include producing valuable halogenoalkanes from alkanes. Chlorination of alkanes, for example, can give a mixture of mono-, di-, tri- and tetra-chlorinated products. Radicals provide a route to useful products, but mixtures can be formed which may be difficult to separate. Reactions may be uncontrollable and of little use in preparing valuable organic molecules such as insecticides and pharmaceuticals.
	Why use radicals?
	There are many efficient organic reactions involving ions such as R3C+ or R3C– as intermediates (R represents an alkyl group). These ions are generally prepared under acidic or basic conditions. This can be a problem for acid-sensitive or base-sensitive reagents because, rather than forming the desired ion, the reagent can decompose. For radical reactions this is much less of a problem because radicals are formed under mild and neutral conditions.
	Radical reactions are not very sensitive to changes in solvent. The formation of intermediate ions often requires a polar solvent which can solvate and stabilise the ions. Because radicals are neutral they are generally not solvated and changing the solvent will be less important.
	Finally, most radicals are highly reactive and can be used for changes that are difficult or impossible to achieve using ions. This includes halogenation and oxidation of alkanes and preparation of highly strained molecules. So radical reactions do have some important advantages over ionic reactions, but what about controlling them so that only one, rather than many, organic products are formed?
	Getting in control
	Most radical reactions involve chain processes. Efficient chain reactions require a selective initiation step in which only one bond is broken in an initiator molecule. To do this effectively, relatively low temperatures (below 150 °C) need to be used and the organic starting material should contain one particularly weak bond.

	At present, the most important reagent used in radical chain reactions is tributyltin hydride, (C4H9)3SnH. A typical reaction involves heating this compound with an initiator to make the tributyltin radical, (C4H9)3Sn•, which can then react with a variety of organic compounds. Though tributyltin hydride has played a crucial part in the development of radical chemistry, it is relatively expensive and neurotoxic and the tributyltin halide by-products, such as (C4H9)3SnCl, can be difficult to separate from the organic products on a large scale.
	So synthetic chemists faced with the most perplexing problems are now finding that radical reactions can provide the perfect solution.
(589 words)
Adapted from “A radical alternative to ions” by Andrew F. Parsons, Education in Chemistry, March 2003.
	Answer the following questions.
(a)	Explain what is meant by a free radical.
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(1)
(b)	Name the type of bond breaking which occurs when a chlorine molecule forms free radicals.
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(1)
(c)	Suggest the condition which causes chlorine free radicals to be produced from chlorofluorocarbons in the Earth’s atmosphere.
.......................................................................................................................................
(1)
(d)	Write an equation for the reaction between ethane and chlorine to form a dichloroalkane.

(2)
(e)	Tetrafluoroethene is made from an ethene molecule in which each hydrogen atom is replaced by a fluorine atom. Draw a section of the polymer poly(tetrafluoroethene) showing at least two monomer units.

(1)

(f)	Propanone, CH3COCH3 is an example of a polar solvent. Draw a diagram of a molecule of propanone indicating where it is polar.

(1)
(g)	Summarise, in no more than 110 words, the problems and advantages of using radicals in organic synthesis.
	You are NOT asked to summarise the whole passage, nor to include equations in your summary. At the end of your summary state the number of words you have used.
	Credit will be given for answers written in good English, using complete sentences and using technical words correctly and chemical names rather than formulae. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations, units and hyphenated words. Any title you give your passage does not count in your word total.
(8)
	There are penalties for the use of words in excess of 110.
(Total 15 marks)