0620_s10_qp_31
A paper of Chemistry, 0620
Questions:
8
Year:
2010
Paper:
3
Variant:
1
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1
For Examiner’s Use Choose an element which fi ts each of the following descriptions. It is a yellow solid which burns to form an acidic oxide. This element is a black solid which, when heated, forms a purple vapour. Most of its soluble salts are blue. It has a basic oxide of the type MO which is used to treat acidic soils. It is an unreactive gas used to fi ll balloons.
7. Acids, bases and salts  →  7.2. Oxides
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
7. Acids, bases and salts  →  7.1. The characteristic properties of acids and bases
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2
Ozone is a form of oxygen. Ozone is present in the upper atmosphere and it prevents dangerous solar radiation from reaching the Earth’s surface. Some of the chemicals that diffuse into the upper atmosphere decompose ozone. Chemicals that have this effect are methane (CH4), chloromethane (CH3Cl ) and an oxide of nitrogen (NO2). Which of these three chemicals diffuses the most slowly? Give a reason for your choice. Chloromethane is formed when seaweed decomposes. Name the compounds in the environment from which seaweed might have obtained the following elements: carbon; hydrogen; chlorine. How can chloromethane be made from methane? reagent condition For Examiner’s Use The oxides of nitrogen are atmospheric pollutants. Describe how they are formed. Complete the equation for the decomposition of ozone. O3 →
10. Chemistry of the environment  →  10.3. Air quality and climate
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3
For Examiner’s Use A diagram of the apparatus which could be used to investigate the rate of reaction between magnesium and an excess of an acid is drawn below. 100 cm3 of acid 1.0 mol / dm3 volume of hydrogen measured every 15 seconds small piece of magnesium graduated tube hydrogen collects The magnesium kept rising to the surface. In one experiment, this was prevented by twisting the magnesium around a piece of copper. In a second experiment, the magnesium was held down by a plastic net fastened to the beaker. Suggest a reason why magnesium, which is denser than water, fl oated to the surface. Iron, zinc and copper have similar densities. Why was copper a better choice than iron or zinc to weigh down the magnesium? The only difference in the two experiments was the method used to hold down the magnesium. The results are shown below. volume of H2 / cm3 time / s magnesium held down by copper magnesium held down by plastic For Examiner’s Use In which experiment did the magnesium react faster? Suggest a reason why the experiment chosen in had the faster rate. The experiment was repeated using 1.0 mol / dm3 propanoic acid instead of 1.0 mol / dm3 hydrochloric acid. Propanoic acid is a weak acid. How would the graph for propanoic acid differ from the graph for hydrochloric acid? How would the graph for propanoic acid be the same as the graph for hydrochloric acid? Give two factors which would alter the rate of this reaction. For each factor explain why it alters the rate. factor explanation factor explanation
6. Chemical reactions  →  6.2. Rate of reaction
9. Metals  →  9.4. Reactivity series
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4
For Examiner’s Use Hydrolysis is used in chemistry to break down complex molecules into simpler ones. Compounds containing the group are esters. Give the names and formulae of the two compounds formed when the ester ethyl propanoate is hydrolysed. CH2 C O O CH3 CH2 CH3 name name formula formula Fats are naturally occurring esters. They can be hydrolysed by boiling with aqueous sodium hydroxide. C17H35COOCH2 C17H35COOCH2 C17H35COOCH + 3NaOH → 3C17H35COONa + CHOH CH2OH fat CH2OH What type of compound has the formula C17H35COONa and what is its main use? type of compound use Name a synthetic polyester. C or O O COO For Examiner’s Use The structure of a typical protein is drawn below. N C O H H N C O H N C O O H N C What is the name of the polymer linkage? Draw the structural formula of a man-made polymer with the same linkage. A protein can be hydrolysed to a mixture of amino acids which are colourless. Individual amino acids can be identifi ed by chromatography. The Rf value of the amino acid glycine is 0.5. Describe how you could show that glycine was present on a chromatogram.
11. Organic chemistry  →  11.8. Polymers
11. Organic chemistry  →  11.2. Naming organic compounds
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Carbon and silicon are elements in Group IV. Both elements have macromolecular structures. Diamond and graphite are two forms of the element carbon. Explain why diamond is a very hard substance. Give one use of diamond. For Examiner’s Use Explain why graphite is a soft material. Give one use of graphite. Two of the oxides of these elements are carbon dioxide, CO2, and silicon(oxide, SiO2. Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound carbon dioxide. Use x to represent an electron from a carbon atom. Use o to represent an electron from an oxygen atom. A section of the macromolecular structure of silicon(oxide is given below. Si O O O O Use this diagram to explain why the formula is SiO2 not SiO4. Predict two differences in the physical properties of these two oxides.
2. Atoms, elements and compounds  →  2.6. Giant covalent structures
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6
For Examiner’s Use Iodine reacts with chlorine to form dark brown iodine monochloride. I2 + Cl2 → 2ICl This reacts with more chlorine to give yellow iodine trichloride. There is an equilibrium between these iodine chlorides. ICl + Cl2ICl 3dark brown yellow Explain what is meant by equilibrium. When the equilibrium mixture is heated it becomes a darker brown colour. Is the reverse reaction endothermic or exothermic? Give a reason for your choice. The pressure on the equilibrium mixture is decreased. How would this affect the position of equilibrium and why? It would move to the reason Describe what you would observe.
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
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7
For Examiner’s Use Titanium is a transition element. It is isolated by the following reactions. titanium ore → titanium(oxide → titanium(chloride → titanium TiO2 TiCl 4 Ti Why is it usually necessary to include a number in the name of the compounds of transition elements? Titanium(chloride is made by heating the oxide with coke and chlorine. TiO2 + 2Cl 2 TiCl 4 + O2 2C + O2 2CO Explain why the presence of coke ensures the maximum yield of the metal chloride. Explain why the change, titanium(chloride to titanium, is reduction. Complete the table which shows some of the properties of titanium and its uses. The fi rst line has been completed as an example. property related use soluble in molten steel making steel titanium alloys making aircraft and space vehicles resistant to corrosion, especially in sea water For Examiner’s Use The titanium ore contains 36.8% iron, 31.6% titanium and the remainder is oxygen. Determine the percentage of oxygen in this titanium compound. percentage of oxygen = % Calculate the number of moles of atoms for each element. The number of moles of Fe is shown as an example. number of moles of Fe = 36.8 / 56 = 0.66 number of moles of Ti = number of moles of O = What is the simplest ratio for the moles of atoms? Fe : Ti : O What is the formula of this titanium compound?
9. Metals  →  9.6. Extraction of metals
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8
For Examiner’s Use Methanoic acid is the fi rst member of the homologous series of carboxylic acids. Give two general characteristics of a homologous series. In some areas when water is boiled, the inside of kettles become coated with a layer of calcium carbonate. This can be removed by adding methanoic acid. Complete the equation. HCOOH + CaCO3 → Ca(HCOO)2 + + Methanoic acid reacts with most metals above hydrogen in the reactivity series. Complete the word equation. zinc + methanoic acid → + Aluminium is also above hydrogen in the reactivity series. Why does methanoic acid not react with an aluminium kettle? Give the name, molecular formula and empirical formula of the fourth acid in this series. name molecular formula empirical formula
9. Metals  →  9.4. Reactivity series
7. Acids, bases and salts  →  7.1. The characteristic properties of acids and bases
11. Organic chemistry  →  11.7. Carboxylic acids
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