3 Equilibrium constant Ka

 

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Oxford Textbook Pages : 319 - 325

CGP Revision Guide Pages : 138 - 139

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Show Specification Ref : 5.1.3c, 5.1.3g, 5.1.3h

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Question 1 / 5

AQA Jan 2013 Paper 1 Q4 the following table shows the boiling points of some straight chain alkanes do not write outside the box ch c h c h c h c h boiling point c a state a process used to separate an alkane from a mixture of these alkanes mark b both c h and c h can be liquefied and used as fuels for camping stoves suggest with a reason which of these two fuels is liquefied more easily mark c write an equation for the complete combustion of c h mark d explain why the complete combustion of c h may contribute to environmental problems mark e balance the following equation that shows how butane is used to make the compound called maleic anhydride ch ch ch ch o c h co o h o mark wmp jan chem do not write outside the box f ethanethiol c h sh a compound with an unpleasant smell is added to gas to enable leaks from gas pipes to be more easily detected f i write an equation for the combustion of ethanethiol to form carbon dioxide water and sulfur dioxide mark f ii identify a compound that is used to react with the sulfur dioxide in the products of combustion before they enter the atmosphere give one reason why this compound reacts with sulfur dioxide substance reason marks f iii ethanethiol and ethanol molecules have similar shapes explain why ethanol has the higher boiling point marks question continues on the next page turn over wmp jan chem g the following compound x is an isomer of one of the alkanes in the table on page do not write outside the box c c g i give the iupac name of x mark g ii x has a boiling point of c explain why the boiling point of x is lower than that of its straight chain isomer marks g iii the following compound y is produced when x reacts with chlorine cl cl c c deduce how many other position isomers of y can be formed write the number of other position isomers in this box mark wmp jan chem do not write outside the box h cracking of one molecule of an alkane z produces one molecule of ethane one molecule of propene and two molecules of ethene h i deduce the molecular formula of z mark h ii state the type of cracking that produces a high proportion of ethene and propene give the two conditions for this cracking process type of cracking conditions marks turn over for the next question turn over wmp jan chem
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Question 2 / 5

AQA Jun 2010 Paper 2 Q2 do not write outside the box a a student carried out an experiment to study the rates of hydrolysis of some haloalkanes in the experiment two different haloalkanes were placed in separate test tubes containing silver nitrate solution the haloalkanes reacted with the water in the silver nitrate solution the student timed how long it took for the first appearance of the silver halide precipitate in each tube at a constant temperature this time was used to provide a measure of the initial rate of reaction the student obtained the following results time to form a precipitate s bromobutane iodobutane a i state the meaning of the term hydrolysis mark a ii state the colour of the precipitate formed when iodide ions react with silver nitrate and write the simplest ionic equation for this reaction colour of precipitate simplest ionic equation marks a iii use your knowledge of the reactions of halide ions with silver nitrate to suggest why the student did not include fluorobutane in this experiment marks wmp jun chem do not write outside the box b the student used the following enthalpy data to try to account for the different initial rates of hydrolysis of the haloalkanes used in part a the student deduced that the rate of hydrolysis of a haloalkane is influenced by the strength of the carbon halogen bond in the haloalkane bond enthalpy kj mol c br c i state how the experimental evidence enabled the student to make this deduction mark c the student had read that the reaction of water with haloalkanes was similar to the reaction of aqueous sodium hydroxide with haloalkanes and was an example of a nucleophilic substitution reaction c i state the meaning of the term nucleophile mark c ii when a hydroxide ion collides with a molecule of bromobutane the following reaction occurs ch ch ch ch br oh ch ch ch ch oh br outline the nucleophilic substitution mechanism for this reaction question continues on the next page marks turn over wmp jun chem do not write outside the box d the reaction of hydroxide ions with bromo methylpropane may occur by a different mechanism from the one in part c this different mechanism involves the formation of a carbocation d i complete the following equation by drawing the structure of the carbocation formed when the c br bond in bromo methylpropane is broken ch ch c br ch br mark d ii suggest one reason why this reaction occurs by a mechanism involving a carbocation but the reaction in part c ii does not mark wmp jun chem
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Question 3 / 5

AQA Jan 2010 Paper 4 Q2 areas outside the box will not be scanned for marking in this question give all values of ph to decimal places a i write an expression for the term ph mark a ii calculate the concentration in mol dm of an aqueous solution of sulfuric acid that has a ph of marks b a student carried out a titration by adding an aqueous solution of sodium hydroxide from a burette to an aqueous solution of ethanoic acid the end point was reached when cm of the sodium hydroxide solution had been added to cm of mol dm ethanoic acid b i write an equation for the reaction between sodium hydroxide and ethanoic acid mark b ii calculate the concentration in mol dm of the sodium hydroxide solution used marks wmp jan chem b iii a list of indicators is shown below areas outside the box will not be scanned for marking indicator thymol blue bromophenol blue litmus cresol purple ph range select from the list the most suitable indicator for the end point of this titration mark b iv suggest why the concentration of sodium hydroxide in a solution slowly decreases when left open to air mark c at k the value of the acid dissociation constant ka for ethanoic acid in aqueous solution is mol dm c i write an expression for the acid dissociation constant ka for ethanoic acid mark c ii calculate the ph of mol dm ethanoic acid at this temperature marks extra space question continues on the next page turn over wmp jan chem areas outside the box will not be scanned for marking c iii calculate the ph of the buffer solution formed when cm of mol dm potassium hydroxide are added to cm of mol dm ethanoic acid marks extra space wmp jan chem there are no questions printed on this page do not write on this page answer in the spaces provided turn over wmp jan chem
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Question 4 / 5

AQA Jan 2011 Paper 4 Q2 do not write outside the box this question is about the ph of several solutions give all values of ph to decimal places a i write an expression for ph mark a ii calculate the ph of mol dm hydrochloric acid mark a iii calculate the ph of the solution formed when cm of mol dm hydrochloric acid are added to cm of water marks b the acid dissociation constant ka for the weak acid hx has the value x mol dm at c a solution of hx has a ph of calculate the concentration of hx in the solution marks question continues on the next page turn over wmp jan chem do not write outside the box c explain why the ph of an acidic buffer solution remains almost constant despite the addition of a small amount of sodium hydroxide marks d the acid dissociation constant ka for the weak acid hy has the value x mol dm at c a buffer solution was prepared by dissolving mol of the salt nay in cm of a mol dm solution of the weak acid hy d i calculate the ph of this buffer solution marks wmp jan chem do not write outside the box d ii a x mol sample of sodium hydroxide was added to this buffer solution calculate the ph of the buffer solution after the sodium hydroxide was added marks turn over for the next question turn over wmp jan chem
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Question 5 / 5

AQA Jun 2013 Paper 4 Q5 do not write outside the box lactic acid ch ch oh cooh is formed in the human body during metabolism and exercise this acid is also formed by the fermentation of carbohydrates such as sucrose c h o a i give the iupac name for lactic acid mark a ii write an equation for the formation of lactic acid from sucrose and water mark b a molecule of lactic acid contains an asymmetric carbon atom the lactic acid in the body occurs as a single enantiomer a racemic mixture racemate of lactic acid can be formed in the following two stage synthesis ch c o stage hcn ch c cn oh stage ch c cooh oh b i name and outline a mechanism for stage name of mechanism mechanism marks wmp jun chem do not write outside the box b ii give the meaning of the term racemic mixture racemate mark b iii explain how you could distinguish between a racemic mixture racemate of lactic acid and one of the enantiomers of lactic acid marks c a mixture of lactic acid and its salt sodium lactate is used as an acidity regulator in some foods an acidity regulator makes sure that there is little variation in the ph of food c i write an equation for the reaction of lactic acid with sodium hydroxide mark c ii the acid dissociation constant ka for lactic acid has the value mol dm at k calculate the ph of an equimolar solution of lactic acid and sodium lactate marks question continues on the next page turn over wmp jun chem do not write outside the box c iii suggest an alternative name for the term acidity regulator explain how a mixture of lactic acid and sodium lactate can act as a regulator when natural processes increase the acidity in some foods name explanation marks extra space d the cup shown is made from pla poly lactic acid pla is the condensation polymer formed from lactic acid the polymer is described as biodegradable and compostable compostable material breaks down slowly in contact with the moist air in a garden bin this produces compost that can be used to improve soil the manufacturers stress that pla cups differ from traditional plastic cups that are neither biodegradable nor compostable d i draw a section of pla that shows two repeating units marks wmp jun chem do not write outside the box d ii name the type of condensation polymer in pla mark d iii an intermediate in the production of pla is a cyclic compound c h o that is formed from two pla molecules draw the structure of this cyclic compound d iv traditional non biodegradable plastic cups can be made from poly phenylethene commonly known as polystyrene draw the repeating unit of poly phenylethene mark mark d v the manufacturers of pla claim that the material will break down to compost in just weeks suggest one reason why pla in landfill may take longer than weeks to break down mark turn over wmp jun chem
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