0620_w12_qp_31
A paper of Chemistry, 0620
Questions:
7
Year:
2012
Paper:
3
Variant:
1
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1
For Examiner’s Use A list of techniques used to separate mixtures is given below. fi ltration diffusion fractional distillation simple distillation crystallisation chromatography From this list, choose the most suitable technique to separate the following mixtures. A technique may be used once, more than once or not at all. butane from a mixture of propane and butane oxygen from liquid air water from aqueous magnesium sulfate potassium chloride from aqueous potassium chloride silver chloride from a mixture of silver chloride and water glucose from a mixture of glucose and maltose
12. Experimental techniques and chemical analysis  →  12.4. Separation and purification
12. Experimental techniques and chemical analysis  →  12.3. Chromatography
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2
For Examiner’s Use Three of the halogens in Group VII are listed below. chlorine bromine iodine How does their colour change down the Group? How do their melting points and boiling points change down the Group? Predict the colour and physical state (solid, liquid or gas) of astatine, At. colour physical state A radioactive isotope of iodine, I 131 , is used to treat cancer. Defi ne the term isotope. How many protons, electrons and neutrons are there in one atom of I 131 ? number of protons number of electrons number of neutrons When this isotope, I 131 , emits radiation, a different element with a proton number of 54 is formed. What is the name of this element? Fluorine, the most reactive halogen, forms compounds with the other halogens. It forms two compounds with bromine. Deduce their formulae from the following information. compound 1 The mass of one mole of this compound is 137 g. Its formula is compound 2 0.02 moles of this compound contain 0.02 moles of bromine atoms and 0.1 moles of fl uorine atoms. Its formula is
8. The Periodic Table  →  8.3. Group VII properties
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3
For Examiner’s Use The speed of a chemical reaction depends on a number of factors which include temperature and the presence of a catalyst. Reaction speed increases as the temperature increases. Explain why reaction speed increases with temperature. Reactions involving enzymes do not follow the above pattern. The following graph shows how the speed of such a reaction varies with temperature. speed temperature Suggest an explanation why initially the reaction speed increases then above a certain temperature the speed decreases. An organic compound decomposes to give off nitrogen. C6H5N2Cl → C6H5Cl + N2The speed of this reaction can be determined by measuring the volume of nitrogen formed at regular intervals. Typical results are shown in the graph below. time volume of nitrogen The reaction is catalysed by copper. Sketch the graph for the catalysed reaction on the diagram above. For Examiner’s Use How does the speed of this reaction vary with time? Why does the speed of reaction vary with time? Catalytic converters reduce the pollution from motor vehicles. oxides of nitrogen and carbon monoxide less harmful gases to atmosphere catalysts: rhodium, platinum, palladium Describe how carbon monoxide and the oxides of nitrogen are formed in car engines. Describe the reactioninside the catalytic converter which change these pollutants into less harmful gases. Include at least one equation in your description.
6. Chemical reactions  →  6.2. Rate of reaction
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4
For Examiner’s Use Silicon(oxide, SiO2, and zirconium(oxide, ZrO2, are both macromolecules. They have similar physical properties but silicon(oxide is acidic and zirconium(oxide is amphoteric. Defi ne the term macromolecule. Predict three physical properties of these two oxides. Name an element which has the same physical properties as these two oxides. Name a reagent that reacts with the oxides of both elements. Name a reagent that reacts with only one of the oxides. reagent oxide which reacts
2. Atoms, elements and compounds  →  2.6. Giant covalent structures
7. Acids, bases and salts  →  7.2. Oxides
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5
For Examiner’s Use Carbonyl chloride, COCl 2, is widely used in industry to make polymers, dyes and pharmaceuticals. Carbonyl chloride was fi rst made in 1812 by exposing a mixture of carbon monoxide and chlorine to bright sunlight. This is a photochemical reaction. CO+ Cl 2→ COCl 2Explain the phrase photochemical reaction. Give another example of a photochemical reaction and explain why it is important either to the environment or in industry. Carbonyl chloride is now made by the reversible reaction given below. CO+ Cl 2COCl 2The forward reaction is exothermic. The reaction is catalysed by carbon within a temperature range of 50 to 150 °C. Predict the effect on the yield of carbonyl chloride of increasing the pressure. Explain your answer. If the temperature is allowed to increase to above 200 °C, very little carbonyl chloride is formed. Explain why. Explain why a catalyst is used. For Examiner’s Use The structural formula of carbonyl chloride is given below. C O Cl Cl Draw a diagram showing the arrangement of the outer electrons in one molecule of this covalent compound. Use o to represent an electron from a carbon atom. Use x to represent an electron from a chlorine atom. Use ● to represent an electron from an oxygen atom.
11. Organic chemistry  →  11.4. Alkanes
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
6. Chemical reactions  →  6.2. Rate of reaction
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6
For Examiner’s Use A sandwich contains three of the main constituents of food. bread contains complex carbohydrates butter contains fat meat contains protein These constituents of food can be hydrolysed by boiling with acid or alkali. Complete the table. constituent of food product of hydrolysis protein fat complex carbohydrate What type of synthetic polymer contains the same linkage as fats, proteins? An incomplete structural formula of a protein is given below. Complete this diagram by inserting the linkages. insert linkage insert linkage Butter contains mainly saturated fats. Fats based on vegetable oils, such as olive oil, contain mainly unsaturated fats. A small amount of fat was dissolved in an organic solvent. Describe how you could determine if the fat was saturated or unsaturated.
7. Acids, bases and salts  →  7.1. The characteristic properties of acids and bases
11. Organic chemistry  →  11.8. Polymers
11. Organic chemistry  →  11.5. Alkenes
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7
For Examiner’s Use Both strontium and sulfur have chlorides of the type XCl 2. The table below compares some of their properties. strontium chloride sulfur chloride appearance white crystals red liquid formula SrCl 2 SCl 2 melting point / °C –120 boiling point / °C conductivity of liquid good poor solubility in water dissolves to form a neutral solution reacts to form a solution of pH 1 Use the data in the table to explain why sulfur chloride is a liquid at room temperature, 25 °C. Strontium is a metal and sulfur is a non-metal. Explain why both have chlorides of the type XCl 2. The electron distribution of a strontium atom is 2 + 8 + 18 + 8 + 2. Deduce the name of the acidic compound formed when sulfur chloride reacts with water. Explain the difference in the electrical conductivity of liquid strontium chloride and liquid sulfur chloride. For Examiner’s Use Strontium chloride-6-water can be made from the insoluble compound, strontium carbonate, by the following reactions. SrCO3+ 2HCl → SrCl 2+ CO2+ H2OSrCl 2 + 6H2O→ SrCl 2.6H2OThe following method was used to prepare the crystals. Add excess strontium carbonate to hot hydrochloric acid. Filter the resulting mixture. Partially evaporate the filtrate and allow to cool. Filter off the crystals of SrCl 2.6H2O. Dry the crystals between filter papers. How would you know when excess strontium carbonate had been added in step 1? Why is it necessary to fi lter the mixture in step 2? In step 3, why partially evaporate the fi ltrate rather than evaporate to dryness? In the above experiment, 50.0 cm3 of hydrochloric acid of concentration 2.0 mol / dm3 was used. 6.4 g of SrCl 2.6H2O was made. Calculate the percentage yield. number of moles of HCl used = number of moles of SrCl 2.6H2O which could be formed = mass of one mole of SrCl 2.6H2O is 267 g theoretical yield of SrCl 2.6H2O = g percentage yield = %
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
9. Metals  →  9.4. Reactivity series
4. Electrochemistry  →  4.1. Electrolysis
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