CHEMISTRY (SALTERS) 2849

Transcription

1 XFRD CAMBRIDGE AND RSA EXAMINATINS Advanced GCE CHEMISTRY (SALTERS) 2849 Chemistry of Materials Thursday 23 JUNE 2005 Afternoon 1 hour 30 minutes Candidates answer on the question paper. Additional materials: Data Sheet for Chemistry (Salters) Scientific calculator Candidate Name Centre Number Candidate Number TIME 1 hour 30 minutes INSTRUCTINS T CANDIDATES Write your name in the space above. Write your Centre number and Candidate number in the boxes above. Answer all the questions. Write your answers in the spaces provided on the question paper. Read each question carefully and make sure you know what you have to do before starting your answer. INFRMATIN FR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You will be awarded marks for the quality of written communication where this is indicated in the question. You may use a scientific calculator. You may use the Data Sheet for Chemistry (Salters). You are advised to show all the steps in any calculations. FR EXAMINER S USE Qu. Max. Mark TTAL 90 This question paper consists of 15 printed pages and 1 blank page. SPA (MML /04) S75155/5 CR 2005 [R/100/3432] Registered Charity Number: [Turn over

2 2 Answer all the questions. 1 Acetanilide was introduced in the 1880s as a medicine for reducing the pain and high temperature effects of a fever. It can be made from phenylamine. H C NH 2 N CH 3 phenylamine acetanilide (a) (i) Name the functional group in acetanilide that is attached to the benzene ring.... [1] (ii) What reagent would you use to convert phenylamine into acetanilide?... [1] (b) Acetanilide is readily hydrolysed by heating with an aqueous solution of sodium hydroxide. Two organic products are formed, compound A and a salt B. hydrolysis acetanilide compound A + salt B an amine A mass spectrum of compound A is shown below intensity / % mass

3 (i) What is the M r of compound A? 3 M r =... [1] (ii) The mass spectrometer breaks the molecule into fragments. What is the mass of the fragment lost when the ion of mass 77 is formed? mass =... [1] (iii) Suggest a formula for the fragment having the mass calculated in b(ii).... [1] (iv) Give the structural formula of the ion responsible for the peak at 77. (v) Draw the structure of the hydrolysis product, compound A. [2] [2] (vi) Compound A is soluble in acid but insoluble in alkali. Explain why compound A is soluble in acid. (c) The salt B is soluble in water. n adding excess hydrochloric acid, a liquid C is formed which is distilled off. The table below gives the chemical shifts and their relative intensities for the peaks in the proton n.m.r. spectrum of the liquid C. chemical shift relative number of protons type of proton Complete the table and give the structure of the compound C. [3] [Turn over

4 (d) (e) 4 In this question, one mark is available for the quality of spelling, punctuation and grammar. A solid sample is thought to be impure acetanilide. The sample is soluble in ethanol. Describe how thin-layer chromatography would be carried out to show that acetanilide is present in the sample... [6] Quality of Written Communication [1] At the start of the 20th century, the discovery and testing of a new medicine was a very random process. Today, medicine development is much longer and costs more. ften it takes 10 to 12 years to get a new product on the market. Describe two ways in which chemists are involved in the development of a new medicine... [2] [Total: 23]

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6 2 Steel alloys containing large amounts of titanium are corrosion resistant, have low densities and good strength properties. 6 (a) Suggest how adding a large amount of an alloying element to iron affects the structure of iron... [1] (b) Titanium alloys are often used for reaction vessels in the chemical industry because of their high chemical resistance. However, they cannot be used with concentrated hydrochloric acid. This reacts with titanium to form a mixture of coloured ions. (i) Why do many transition metal ions appear coloured? (ii) ne of the coloured ions formed when titanium reacts with hydrochloric acid is the hexaaquatitanium(iii) ion, [Ti(H 2 ) 6 ] 3+ (aq). In the box below, draw the shape of this complex ion indicating the charge on the ion. Give the name for the shape of this complex ion. shape of complex ion... [3]

7 7 (iii) The [Ti(H 2 ) 4 Cl 2 ] + ion is also formed in concentrated hydrochloric acid. Suggest why there are two possible structures for this ion. (c) A solution of the hexaaquatitanium(iii) ion is acidic. The equation for this is given below. [Ti(H 2 ) 6 ] 3+ (aq) [Ti(H 2 ) 5 (H)] 2+ (aq) + H + (aq) The equilibrium expression for this reaction is given below. [[Ti(H 2 ) 5 (H)] 2+ (aq)] [H + (aq)] K c = [[Ti(H 2 ) 6 ] 3+ (aq)] The numerical value of K c at 25 C is (i) Give the units of K c.... [1] (ii) A solution contains mol dm 3 hexaaquatitanium(iii) ions at equilibrium at 25 C. Calculate the concentration of the H + (aq) ions. Give your answer to an appropriate number of significant figures. Assume that [H + (aq)] = [[Ti(H 2 ) 5 (H)] 2+ (aq)]. [H + (aq)] =... mol dm 3 [3] [Total: 12] [Turn over

8 3 X-ray film is made by coating a plastic sheet with a silver halide. The plastic sheet is made from a mixture of a polyester and a nylon. 8 (a) A typical polyester used in the making of films is PET. A repeating unit is shown below. n PET Draw the full structural formula of the alcohol used as a monomer to make PET. [2] (b) A nylon can be made by polymerising a mixture of the monomers D and E. HC(CH 2 ) 4 CH H 2 N(CH 2 ) 6 NH 2 (i) Give the systematic name of compound E. D E (ii) Nylon polymers are formed by a condensation reactions. the reaction between compounds D and E to explain the meaning of condensation.

9 (c) (d) Nylon is added to polyester to make X-ray film stronger. Explain, in terms of intermolecular attractions, why the addition of nylon strengthens the film... [2] (i) Large amounts of used film are disposed of every year. After the silver halide has been removed from the film, the remaining polymer sheets can be disposed of by burning or by burying them in the ground. Give one advantage for each method relative to the other. burning... burying... (ii) Chemists are developing methods to convert some waste polymers into useful chemicals. Polyesters can be broken down by hydrolysis into organic acids and alcohols. Give the conditions and reagent used for hydrolysing an ester link. conditions... reagent... [2] (iii) Unused silver bromide can be recovered from waste films. The amount of silver bromide in a sample can be determined by oxidising the bromide ions (Br ) to bromine (Br 2 ), using bromate(v) ions (Br 3 ) as the oxidising agent. Give an overall balanced equation for this redox reaction by combining the half-equations given below. working space 9 2Br (aq) Br 2 (aq) + 2e 2Br 3 (aq) + 12H + (aq) + 10e Br 2 (aq) + 6H 2 (l) [2] [Turn over

10 (e) (f) 10 A student studied the rate of the reaction between bromide ions and bromate(v) ions in acid solution by measuring the concentration of bromine produced at different times. The student planned to use a colorimeter to measure the concentration of the bromine solution. He was given a bromine solution of known concentration. Describe how he would use it to produce a calibration curve to convert absorbance readings from the colorimeter into concentrations... [4] The results obtained for the initial rates of reaction at different concentrations of bromide ion, bromate(v) ion and acid are given below. initial concentration/mol dm 3 [Br (aq)] [Br 3 (aq)] [H + (aq)] initial rate of formation of bromine (relative values)

11 (i) 11 Complete the table below, stating the order of reaction with respect to each reactant. reactant order bromide ion, Br bromate(v) ion, Br 3 acid, H + [3] (ii) your answers to (i) to complete the rate equation for this reaction. Give the units of the rate constant if the rate of reaction is measured in mol dm 3 s 1. rate = units of rate constant... [2] [Total: 23] [Turn over

12 4 At the beginning of the 19th century, batteries were often called voltaic piles after their inventor, Volta. A common battery at this time consisted of strips of zinc separated from strips of silver by layers of paper soaked in salt water. 12 (a) (i) the standard electrode potential data given in the table below to calculate the voltage produced by a standard zinc-silver cell. half-reaction Zn e Zn E /V 0.76 Ag + + e Ag E cell =...V [1] (ii) Suggest a reason why the voltage from a zinc-silver cell in a voltaic pile would be unlikely to have the value calculated in (i).... [1] (iii) Explain why zinc is the negative electrode in a zinc-silver cell. (b) Draw a labelled diagram to show how you would measure the voltage of a zinc-silver cell under standard conditions. [5]

13 (c) 13 A standard hydrogen electrode is used to measure the standard electrode potential of a silver half-cell. Give the equation for the reaction taking place at the hydrogen electrode when the standard electrode potential of the silver half-cell is being measured. (d) Zinc is a d-block element. Complete the electronic configuration for zinc and explain why it does not readily form Zn 3+ ions. [2] Zn 1s 2 2s 2 2p explanation.. [3] [Total: 14] [Turn over

14 5 Wool and silk are both proteins. However, the primary, secondary and tertiary structures of the molecules in wool differ significantly from those in silk. It is these differences that give wool and silk their characteristic properties. 14 (a) The secondary structure of proteins involves hydrogen bonding. The diagram below shows two parts of a folded protein chain. C H R H N C CH N C CH N C CH R H R H R H R N C CH N C CH N C CH N H R H (i) Draw a dashed line on the diagram to show one way in which hydrogen bonding occurs between the two parts of the chain. Include partial charges on the atoms involved. [2] (ii) Proteins contain chiral centres. n the diagram above, mark, with an asterisk, (*), one chiral centre. Explain your choice. (iii) Name two types of secondary protein structure.... and... [2] (b) The tertiary structure of a protein is determined by the position in space of all its atoms. These positions depend on how one part of the folded protein chain can attract or repel other parts. ther than hydrogen bonding, name two types of attraction that can occur between parts of the protein chain... [2]

15 (c) (d) Genetic engineering can be used to produce sufficient quantities of a pure protein so that its tertiary structure can be studied. (i) utline the role played by enzymes in isolating the gene responsible for the synthesis of the protein. (ii) Explain how the gene is used to synthesise the required protein.... [3] The composition of the protein in wool or silk can be determined by hydrolysing the protein and identifying the individual amino acids. (i) 15 Give the reagent needed to hydrolyse a protein.... [1] (ii) The reagent and protein are heated together under reflux. Describe what this means. (e) Another method for investigating structures of proteins is n.m.r. spectroscopy. What information can be obtained from n.m.r. spectra?.. [2] [Total: 18] END F QUESTIN PAPER

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