0620_s05_qp_3
A paper of Chemistry, 0620
Questions:
6
Year:
2005
Paper:
3
Variant:
0
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1
For Examiner's Use Three of the halogens in Group VII are: chlorine bromine iodine How does their colour change down the Group? How does their physical state (solid, liquid or gas) change down the Group? Predict the colour and physical state of fluorine. colour physical state Describe how you could distinguish between aqueous potassium bromide and aqueous potassium iodide. test result with bromide result with iodide 0.015 moles of iodine react with 0.045 moles of chlorine to form 0.030 moles of a single product. Complete the equation. I2 + Cl2 Traces of chlorine can be separated from bromine vapour by diffusion. Which gas would diffuse the faster and why?
8. The Periodic Table  →  8.3. Group VII properties
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For Examiner's Use The following apparatus was used to measure the rate of the reaction between zinc and iodine. 100 cm3 of aqueous iodine, 0.1 mol / dm3 at 25 oC mixture stirred by magnetic stirrer thin plate of zinc to balance The mass of the zinc plate was measured every minute until the reaction was complete. Write an ionic equation for the redox reaction that occurred between zinc atoms and iodine molecules. Describe how you could show by adding aqueous sodium hydroxide and aqueous ammonia that a solution contained zinc ions. result with sodium hydroxide excess sodium hydroxide result with aqueous ammonia excess aqueous ammonia For Examiner's Use From the results of this experiment two graphs were plotted. time time mass of plate loss of mass graph 1 graph 2 Which reagent iodine or zinc was in excess? Give a reason for your choice. Describe how the shape of graph 1 would change if 100cm3 of 0.05 mol/dm3 iodine had been used. On graph 2, sketch the shape if the reaction had been carried out using 100 cm3 of 0.1 mol/dm3 iodine at 35 °C instead of at 25 °C.
9. Metals  →  9.4. Reactivity series
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
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For Examiner's Use A South Korean chemist has discovered a cure for smelly socks. Small particles of silver are attached to a polymer, poly, and this is woven into the socks. Give the structural formula of the monomer. Draw the structural formula of the polymer. Suggest which one, monomer or polymer, will react with aqueous bromine and why? To show that the polymer contains silver the following test was carried out. The polymer fibres were chopped into small pieces and warmed with nitric acid. The silver atoms were oxidised to silver(ions. The mixture was filtered. Aqueous sodium chloride was added to the filtrate and a white precipitate formed. Why was the mixture filtered? Explain why the change of silver atoms to silver ions is oxidation. Give the name of the white precipitate. For Examiner's Use The unpleasant smell is caused by carboxylic acids. Bacteria cause the fats on the skin to be hydrolysed to these acids. Silver kills the bacteria and prevents the hydrolysis of the fats. Fats are esters. Give the name and structural formula of an ester. name structural formula Complete the word equation. Ester + water carboxylic acid + Propanoic acid is a weak acid. The following equation represents its reaction with ammonia. CH3 CH2 COOH + NH3 CH3 CH2 COO– + NH4 + Explain why propanoic acid behaves as an acid and ammonia as a base. Explain the expression weak acid.
9. Metals  →  9.4. Reactivity series
11. Organic chemistry  →  11.5. Alkenes
11. Organic chemistry  →  11.8. Polymers
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For Examiner's Use The Carlsbad caverns in New Mexico are very large underground caves. Although the walls of these caves are coated with gypsum (hydrated calcium sulphate), the caves have been formed in limestone. It is believed that the caves were formed by sulphuric acid reacting with the limestone. Complete the word equation. calcium + sulphuric calcium + + carbonate acid sulphate Describe how you could test the water entering the cave to show that it contained sulphate ions. test result How could you show that the water entering the cave has a high concentration of hydrogen ions? Hydrogen sulphide gas which was escaping from nearby petroleum deposits was being oxidised to sulphuric acid. Complete the equation for this reaction forming sulphuric acid. H2S + O2 Explain why all the hydrogen sulphide should be removed from the petroleum before it is used as a fuel. For Examiner's Use Draw a diagram to show the arrangement of the valency electrons in one molecule of the covalent compound hydrogen sulphide. Use o to represent an electron from a sulphur atom. Use x to represent an electron from a hydrogen atom. Sulphuric acid is manufactured by the Contact Process. Sulphur dioxide is oxidised to sulphur trioxide by oxygen. 2SO2 + O2 2SO3 Name the catalyst used in this reaction. What temperature is used for this reaction? Describe how sulphur trioxide is changed into sulphuric acid. Gypsum is hydrated calcium sulphate, CaSO4.xH2O. It contains 20.9% water by mass. Calculate x. Mr: CaSO4, 136; H2O, 18. 79.1 g of CaSO4 = moles 20.9 g of H2O = moles x =
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
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For Examiner's Use Enzymes are biological catalysts. They are used both in research laboratories and in industry. Enzymes called proteases can hydrolyse proteins to amino acids. The amino acids can be separated and identified by chromatography. The diagram below shows a typical chromatogram. sample A sample B solvent front initial level of solvent samples are placed on this line The Rf value of a sample = distance travelled by sample distance travelled by solvent front Some Rf values for amino acids are: glutamic acid = 0.4 glycine = 0.5 alanine = 0.7 leucine = 0.9 Identify the two amino acids on the chromatogram. A is B is Explain why the chromatogram must be exposed to a locating agent before Rf values can be measured. For Examiner's Use Measuring Rf values is one way of identifying amino acids on a chromatogram. Suggest another. The synthetic polymer, nylon, has the same linkage as proteins. Draw the structural formula of nylon. Enzymes called carbohydrases can hydrolyse complex carbohydrates to simple sugars which can be represented as OH HO . Draw the structure of a complex carbohydrate. For Examiner's Use Fermentation can be carried out in the apparatus drawn below. After a few days the reaction stops. It has produced a 12% aqueous solution of ethanol. aqueous glucose and yeast allows carbon dioxide to escape but prevents air entering Complete the equation. C6H12O6 + glucose ethanol carbon dioxide Zymase catalyses the anaerobic respiration of glucose. Define the term respiration. Suggest a reason why the reaction stops after a few days. Why is it essential that there is no oxygen in the flask? What technique is used to concentrate the aqueous ethanol?
6. Chemical reactions  →  6.2. Rate of reaction
11. Organic chemistry  →  11.6. Alcohols
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For Examiner's Use The position of aluminium in the reactivity series of metals is shown below. magnesium aluminium zinc copper Aluminium is extracted by the electrolysis of its molten oxide. waste gases carbon cathode (–) carbon anode (+) mixture of aluminium oxide and cryolite aluminium 900 oC Name the main ore of aluminium. Why does the molten electrolyte contain cryolite? Oxygen is produced at the positive electrode . Name another gas which is given off at this electrode. Aluminium reacts very slowly with aqueous copper(sulphate. 2Al+ 3CuSO4Al2(SO4)3+ 3CuWhich of the two metals has the greater tendency to form ions? Describe what you would see when this reaction occurs. Explain why aluminium reacts so slowly. For Examiner's Use Complete the following table by writing “reaction” or “no reaction” in the spaces provided. oxide type of oxide reaction with acid reaction with alkali magnesium basic aluminium amphoteric Predict the equations for the decomposition of the following aluminium compounds. Al(OH)3 + aluminium nitrate + +
9. Metals  →  9.6. Extraction of metals
9. Metals  →  9.4. Reactivity series
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