Centre Number 71 Candidate Number ADVANCED General Certificate of Education 2007 Chemistry Assessment Unit A2 2 assessing Module 5: Analytical, Transition Metals and Further Organic Chemistry [A2C21] A2C21 WEDNESDAY 30 MAY, AFTERNOON TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 13(a)(v). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided. A2C2S7 2930 For Examiner s use only Question Number Section A 1 10 Section B 11 12 13 14 15 Total
Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following formulae represents the complex formed when excess ammonia solution is added to cobalt(ii) sulphate solution? A [Co(NH 3 ) 4 (H 2 O) 2 ] 2+ B [Co(NH 3 ) 4 ] 2+ C [Co(NH 3 ) 6 ] 2+ D [Co(NH 3 ) 2 (H 2 O) 4 ] 2+ 2 Which one of the following organic compounds gives rise to the largest number of peaks in a high resolution n.m.r. spectrum? A CH 3 CH 2 COCH 2 CH 3 B CH 3 COOH C CH 3 CH 2 Br D CH 3 CH 2 COOCH 3 3 In which one of the following complexes does the transition metal present have an oxidation state of +2? A [Co(NH 3 ) 4 Cl 2 ]Cl B [Cu(CN) 4 ] 3 C K 3 [Fe(CN) 6 ] D [Ni(en) 3 ]Cl 2 4 What is the total number of isomers of dichlorobenzene, C 6 H 4 Cl 2? A 2 B 3 C 4 D 5 A2C2S7 2930 2 [Turn over
5 The magnesium content of a sample of water may be determined by titration with edta using a suitable indicator. Which one of the following statements is incorrect? A One mole of edta reacts with one mole of magnesium ions. B The solution must be buffered at a ph of approximately 10. C The complex formed between edta and magnesium ions is coloured. D The magnesium ions forms a stable complex with the indicator. 6 Sulphur dichloride dioxide, SO 2 Cl 2, reacts with water to form a mixture of only hydrochloric acid and sulphuric acid. Calculate the hydrogen ion concentration of the solution formed when 0.02 mole of SO 2 Cl 2 is dissolved to make 250 cm 3 of solution. A 0.08 mol dm 3 B 0.16 mol dm 3 C 0.24 mol dm 3 D 0.32 mol dm 3 7 In the reaction CH 3 O 2 N CH 3 NO 2 HNO 3 /H 2 SO 4 NO 2 which species attacks the benzene ring? A HNO 3 B NO 2 C NO 2 + D H 2 NO 3 + A2C2S7 2930 3 [Turn over
8 A mixture of two amino acids was subjected to two-way chromatography. After elution with solvent 1 the paper was removed, dried and rotated through 90 and eluted with solvent 2. The resultant chromatogram is shown below. solvent front 1 solvent front 2 original spot The R f values for some amino acids are given. amino acid R f (solvent 1) R f (solvent 2) alanine 0.30 0.65 aspartic acid 0.14 0.37 glycine 0.29 0.42 lysine 0.21 0.52 valine 0.54 0.65 Which two amino acids does the mixture contain? A B C D alanine and aspartic acid alanine and valine glycine and lysine glycine and valine A2C2S7 2930 4 [Turn over
9 50 cm 3 of a gaseous hydrocarbon requires exactly 250 cm 3 of oxygen for complete combustion and produces 150 cm 3 of carbon dioxide. What is the formula of the hydrocarbon? A C 3 H 4 B C 3 H 8 C C 5 H 10 D C 5 H 12 10 Each of the copper compounds below can be reduced to the metal. Which one of the compounds would produce the greatest mass of copper metal if 5.0 g of each compound were reduced? A B C CuO Cu 2 O CuS D CuF 2 A2C2S7 2930 5 [Turn over
Section B Answer all five questions in the spaces provided. 11 Instrumental analysis is commonly used to deduce the identity and structure of unknown organic compounds. An organic compound of molecular formula C 5 H 10 O was subjected to a series of tests. (a) The compound produced the following mass spectrum: 100 43 % abundance m/e Suggest the formulae of two ions which would give rise to the peak at m/e 43. [2] A2C2S7 2930 6 [Turn over
(b) The infra-red spectrum for the compound is shown below: 0 Absorbance Bond Absorption Bond Wavenumber/cm 1 C 100 4000 3000 2000 1500 1000 C H 2850 3300 C O 1000 1300 O H 2500 3500 C O 1680 1750 Identify the functional group which has the largest absorbance. _ [1] (c) Use your answers to parts (a) and (b) to deduce the structural formula of the compound. _ [1] A2C2S7 2930 7 [Turn over
12 Para red is a dye which was detected in cayenne pepper sourced from Uzbekistan. The discovery of this banned dye in foodstuffs led to withdrawal of many products from supermarket shelves. The dye can be prepared as follows: NH 2 A + N 2 Cl OH Para red NO 2 NO 2 (a) (i) Name the reagents used in step A. [2] (ii) Explain why a low temperature must be used in step A. (b) (i) Deduce a possible structure for Para red. [2] (ii) Explain why Para red is coloured. [2] A2C2S7 2930 8 [Turn over
BLANK PAGE (Questions continue overleaf) A2C2S7 2930 9 [Turn over
13 Transition metal chemistry is characterised by redox reactions, colour changes and catalytic activity. (a) The most common oxidation states in iron compounds are +2 and +3. Iron(II) ions are readily oxidised to iron(iii). (i) Define the term oxidation in terms of electron transfer. (ii) Iron(II) ions may be oxidised by bubbling chlorine gas through an aqueous solution of the ions. State the colour change observed and write an equation for the reaction. [3] (iii) State the electron structure of an iron(ii) ion and an iron(iii) ion using spd notation. iron(ii) iron(iii) [2] (iv) Use the above electron structures to explain the relative stabilities of the two ions. A2C2S7 2930 10 [Turn over
(v) Describe how the percentage of iron in aluminium foil may be determined using colorimetry. Your account should include how you would: dissolve the foil oxidise the iron to the +3 oxidation state use a named reagent to produce a strongly coloured complex use a calibration curve to determine the concentration of iron in solution [4] Quality of written communication [2] A2C2S7 2930 11 [Turn over
(b) Trinitrotriammine cobalt(iii), [Co(NO 2 ) 3 (NH 3 ) 3 ], is a yellow crystalline substance which may be prepared by the following method. Dissolve 12.2 g of cobalt(ii) ethanoate tetrahydrate in 100 cm 3 of hot water. Cool the solution in an ice-bath and add 10.4 g of sodium nitrite dissolved in 50 cm 3 of 0.88 ammonia. Cool to 10 C and carefully add 14 cm 3 of 20 volume hydrogen peroxide solution followed by 2 g of activated charcoal. After stirring, the mixture is left for 10 minutes before boiling for 30 minutes. Filter the hot solution to remove the activated charcoal and cool the filtrate in an ice-bath. Filter off the crystals, wash with cold ethanol and dry. (i) Deduce the formula of cobalt(ii) ethanoate tetrahydrate. [2] (ii) State and explain the role of hydrogen peroxide in this preparation. [2] (iii) Suggest the shape of the trinitrotriammine cobalt(iii) complex. (iv) Deduce the coordination number of cobalt in the trinitrotriammine cobalt(iii) complex. (v) 20 volume hydrogen peroxide is so named because one volume of the solution produces 20 times this volume of gaseous oxygen on complete decomposition at 20 C and one atmosphere pressure i.e. 1cm 3 of solution will produce 20 cm 3 of oxygen gas. 2H 2 O 2 (aq) 2H 2 O(l) + O 2 (g) Calculate the concentration of 20 volume hydrogen peroxide in mol dm 3. [3] A2C2S7 2930 12 [Turn over
(c) Aqueous cobalt(ii) ions catalyse the decomposition of chlorate(i) ions, ClO, to form oxygen gas. (i) Use three equations to show the three steps involved in this catalytic decomposition. [3] (ii) Explain whether this catalysis is homogeneous or heterogeneous. A2C2S7 2930 13 [Turn over
14 Cyanides are salts of hydrocyanic acid (hydrogen cyanide). Organic cyanides have the formula RCN and are called nitriles. (a) Potassium cyanide is used to extract gold from its ore according to the following reaction: 4Au(s) + 8CN (aq) + 2H 2 O(l) + O 2 (g) 4[Au(CN 2 )] (aq) + 4OH (aq) (i) Name the type of bond formed between the gold ions and the cyanide ions. (ii) This process was simulated in the laboratory. Calculate the volume of 2 M potassium cyanide solution needed to extract 1 kg of gold from its ore. [3] (b) Cyanogen, C 2 N 2, is a colourless gas with the characteristic smell of bitter almonds. (i) Draw a dot and cross diagram to show the bonding in cyanogen. [2] (ii) State and explain the shape of the cyanogen molecule. [2] (iii) Cyanogen may be prepared by warming potassium cyanide solution with copper(ii) sulphate to form copper(ii) cyanide. Decomposition of copper(ii) cyanide yields copper(i) cyanide and cyanogen. Write the equation for the decomposition of copper(ii) cyanide. [2] A2C2S7 2930 14 [Turn over
(c) Ethanenitrile may be prepared by boiling an alcoholic solution of potassium cyanide with iodomethane. (i) Write the equation for the formation of ethanenitrile. (ii) Assuming this occurs as a single step nucleophilic substitution reaction, suggest the structure of the transition state formed. [1] (iii) Name the reagents required to bring about the following changes. CH 3 CH 2 NH 2 A CH3 CN A B C [3] B C CH 3 COOH CH 3 COONa A2C2S7 2930 15 [Turn over
(d) Potassium thiocyanate is prepared by boiling potassium cyanide solution with sulphur. It is extremely soluble in water and reacts readily with silver nitrate solution to form a precipitate of silver thiocyanate. This reaction may be used, as follows, to determine the chloride content in cheese. Weigh out accurately approximately 1.5 g of cheese into a conical flask. Add 10 cm 3 of water, 25.0 cm 3 of 0.05 M silver nitrate solution (an excess) and 10 cm 3 of concentrated nitric acid. Boil for 10 minutes. Cool and add a further 50 cm 3 of water. The excess silver nitrate is determined by titration with standard potassium thiocyanate solution using an iron(iii) indicator. At the end-point the aqueous iron(iii) ions react with excess thiocyanate ions. (i) Explain the term standard solution. (ii) State the colour observed at the end-point. (iii) State the formula of the iron(iii) complex formed at the end-point. (iv) Write the equation for the reaction between aqueous solutions of silver nitrate and potassium thiocyanate to form the silver thiocyanate precipitate. A2C2S7 2930 16 [Turn over
(v) In an experiment 1.48 g of cheese was analysed as above. The excess silver nitrate required 14.3 cm 3 of 0.05 M potassium thiocyanate solution for complete reaction. Calculate the chloride content, in grams, per gram of cheese. [4] A2C2S7 2930 17 [Turn over
15 Patients suffering from Parkinson s disease have a deficiency of the brain neurones that produce the neurotransmitter dopamine. HO HO CH 2 dopamine CH 2 NH 2 (a) Explain why dopamine should be very soluble in water. [2] (b) Dopamine is a base which behaves as a primary amine. (i) Compare and suggest an explanation for the relative basic strengths of dopamine, ammonia and phenylamine. [3] (ii) Write an equation for the reaction of dopamine with hydrochloric acid. A2C2S7 2930 18 [Turn over
(c) Treatment of Parkinson s disease often involves the use of L-dopa which is the natural precursor of dopamine. HO HO CH 2 CH NH 2 COOH L-dopa (i) Deduce the molecular formula of L-dopa. (ii) Explain why L-dopa is optically active. [2] (iii) Draw the structure of the dipolar ion (zwitterion) formed when L-dopa is dissolved in water. [1] THIS IS THE END OF THE QUESTION PAPER A2C2S7 2930 19
S 1/07 7-164-1 [Turn over