KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
(a) Write the structural formula of:
(i) Methanol (ii)Methanoic acid (b) Write the equation for the reaction between methanoic acid and aqueous sodium hydroxide (c) (i) Name the product formed when methanol reacts with methanoic acid (ii) State one condition necessary for the reaction in (c) (i) above to take place (d) (i) Describe one chemical test that can be used to distinguish between hexane and hexane (ii) State one use of hexane (iii) Hydrogen reacts with hexane to form hexane. Calculate the volume or hydrogen gas required to convert 42g of hexane to hexane at S.T.P ( C=12.0, H=1.0, molar gas volume at S.T.P is = 22.4 litres)
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(a) Name one ore from which copper metal is extracted
(b) The chart below shows a sequence of reactions starting with copper. Study it and answer the questions that follow
(ii) Write an equation for the reaction that takes place in step 5
(iii) State the observations made in steps 4 and 7 Step 4 Step 7 (c) Bronze is an alloy of copper and another metal (i) Name the other metal (ii) Give one use of Bronze
The table below gives standard electrode potentials for the metals represented by the Letters D, E, F and G. study it and answer the questions that follow.
(a) Which metal can be displaced from a solution of its salts by all the other metals in the table? Give a reason
(b) Metals F and G were connected to form a cell as shown in the diagram below
(i) Write the equation for the reactions that occur at electrodes
F G (ii) On the diagram, indicate with an arrow the direction in which electrons would flow on the diagram above (ii) What is the function of the salt bridge? (c) An electric current was passed through a concentrated solution of copper (II) chloride as shown in the diagram below
(i) Explain the observation that would be made on the electrolyte as the experiment progresses
(ii) After sometime, test- tube H was found to contain a mixture of two gases. Explain this observation (iii) Which of the electrodes is the anode? Explain
(a) Distinguish between exothermic and endothermic reaction
(b) Changes of state are either exothermic or endothermic Name a change of state that is: (i) Endothermic (ii) Exothermic (c) When pure water is heated at 1 atmospheric pressure at sea level, the temperature of the water does not rise beyond 100°C. Even with continued heated. Explain this observation.
(d) Study the energy cycle diagram below and answer the questions that follow
(i) What does ΔH1 represent? (ii) Show the relationship between ΔH1, ΔH2 and ΔH3 (e) Butane and propane are constituents of a cooking gas. Which produces more energy per mole on combustion? Explain
Study the flow chart below and answer the questions follow
(a) Identify substance
(i) A (ii) B (b) Name process C (c) Give one use of PVC (d) Write an equation for the reaction in which chlorine gas is produced (e) State and explain the observation that would be made if chlorine gas was bubbled into an aqueous solution of sodium iodide (f) In the preparation of a bleaching agent (Sodium hypochlorite), Excess chlorine gas was bubbled into 15 litres of cold 2 m sodium hydroxide (i) Write an equation for the reaction between chlorine gas and cold dilute sodium Hydroxide (ii) Calculate the: Number of moles of sodium hydroxide used Mass in kilograms of the sodium hypochlorite produced = 1. 1175
(a) what method can be used to separate a mixture of ethanol and propanol?
(b) (i) Explain how a solid mixture of sulphur and sodium chloride can be separated Into solid sulphur and solid chloride (c) The table below gives the solubilities of potassium bromide and potassium sulphate at 00C and 400C
When an aqueous mixture containing 60g of potassium and 7 g of potassium sulphate in 10g of water at 800C was cooled to 00C some crystals were formed
(i) Identify the crystals (ii) Determine the mass of the crystals formed (iii) Name the method used to obtain the crystals (iv) Suggest one industrial application of the method named in (iii) above
The following tests were carried out on three separate portions of a colourless solution S
(a) From the information in test (i), name a cation, which is not present in solution S.
(b) Identify a cation, which is likely to be present in solution S (c) Write an ionic equation for the reaction, which takes place in test (ii) Explain how a sample of CH3CH2CH2OH, could be distinguished from a sample of CH3COOH by means of a chemical reaction (2mks)
expected response
Add solid hydrogen carbonate; CH3COOH produces effervescence; while CH3CH2CH2OH does not (Accept any other carbonate that behaves)
expected response
The ionic end lowers the surface tensions of water , facilitating mixing while the nonionic end (non-polar end) mixes with grease, dislodging it from the fabric. Ammonia can be converted to nitrogen monoxide as shown in the equation below (a) Explain how an increase in temperature would affect the yield of nitrogen monoxide (2mks) (b) On the energy level diagram above sketch, the energy level diagram that would be obtained if the reaction is carried out in the presence of platinum catalyst. (1 mk)
answer
(a) Solid dissolves
(b) addition of hydrochloric acid favour backward reaction
Iron is extracted from its ore by the blast furnace process
(a) Name one ore from which iron is extracted (b) One of the impurities in iron is removed in the form of calcium silicate. Write an equation for the reaction in which calcium silicate is produced
The graph below represents a radioactive decay series for isotope H. Study it and answer the questions that follow
(a) Name the type of radiation emitted when isotope H changes to isotope J.
(b) Write an equation for the nuclear reaction that occur when isotope J changes to isotope K
(c) Identify a pair of isotope of an element in the decay series
Use the reactions given below to answer the questions that follow. The letters do not represent the actual symbols of the elements
(a) What name is given to the type of reaction given above?
(b) Arrange the elements D, E, F and G in the order of their reactivity starting with the most reactive (c) Complete the equation below State and explain how the rate of reaction between zinc granules and steam can be increased
answer
The flow charts below show an analysis of a mixture R that contains two salts. Study the analysis and answer the questions that follow. (a) (i) What condition is necessary for the process in step I to take place?(1mk) (ii) Draw a labeled diagram for the set-up that could be used to separate the mixture formed in step II (2mks) (iii) Write ionic equation for the reaction between the cation in filtrate X and aqueous ammonia. (1mk) (iv) What observation would indicate the presence of NO2 (g) in step I (v) State how water vapour, in step I could be identified. (1mk) (b) (i) What conclusion can be drawn from step IV only? Explain? (2mks) (ii) Write the formula of an anion present in the residue U. Explain? (2mks) (iii) Suggest the identity of the cation present in solution z. (1mk) (c) Name the two salts present in the mixture R. (2mks) The flow chart below outlines some of the process involved during extraction of copper from copper pyrites. Study it and answer the questions that follow. (i) Name gas K (1mk) (b) The copper obtained from chamber N is not pure. Draw a labeled diagram to show the set up you would use to refine the copper by electrolysis. (3mks) (c) Given that the mass of copper obtained from above extraction was 210kg, determine the percentage purity of the ore(copper pyrites) if 810kg of it was fed to the 1st roasting furnace. (Cu = 63.5, Fe = 56.0, s=32.0) (3mks) (d) Give two effects that this process could have on the environment (2mks) In an experiment to determine the heat of combustion of methanol, CH2OH a student used a set up like the one shown in the diagram below. a) Write an equation for the combustion of methanol b) Calculate: (i) The number of moles of methanol used in this experiment (C = 12; O = 16; H = 1) (ii) The heat of combustion per mole of methanol. (1mk) (iii) The heat of combustion per mole of methanol (2mks) (c) Explain why the value of the molar heat of combustion for methanol obtained in this experiment is different from the theoretical value. (d) On the axis below draw an energy level diagram for the combustion of methanol. a) 100gm of radioactive 233 Pa was reduced to 12.5g after 81 days. 91 Determine the half-life of Pa. (2mks) b) 233 Pa decays by beta emission. What is the mass number and 91 Atomic number of the element formed? (1mk) Explain the following observation. A chloride dissolves in water to form an electrolyte while the same chloride dissolves in methylbenzene to for a non – electrolyte. (1mk)
Expected Response
The chloride form ions in water which conduct electric current. NO ions are formed in methylbenzene /chloride exists in methylbenzene as molecules. (2mks)
Explain why the enthalpy of neutralization of ethanoic acid with sodium hydroxide is different from that of hydrochloric acid with sodium hydroxide. (2mks)
Expected Response
Enthalpy of neutralization between CH3CaOH(aq) and NaOH(aq) is lower than thatbetween HCl(aq) and NaOH because CH3CaOH(aq) is a weak acid which does not dissociate fully in water thus some of heat produced is used for dissociation fully dissociated and partially dissociated. (2mks) |
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