KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
a) State how burning can be used to distinguish between ethane and ethyne.
Explain your answer. b) Draw the structural formula of the third member of the homologous series of ethyne. c) The flow chart below shows a series of reactions starting with ethanol. Study it and answer the questions that follow.
ii) Write the equation for the combustion of ethanol
iii) Explain why it is necessary to use high pressure to change gas B into the polymer iv) State one use of methane
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The set – up below was used to prepare hydrogen gas
a) Complete the diagram to show how a dry sample of hydrogen gas can be collected
b) Write an equation for the reaction, which takes place when hydrogen gas burns in air. c) i)1.2 litres of hydrogen gas produced at room temperature and pressure when 3.27g of zinc was used. Determine the relative atomic mass of zinc.(Molar gas volume is 24 litres) d) State two industrial uses of hydrogen gas.
The basic raw material for extraction of aluminium is bauxite
a) Name the method that is used to extract aluminium from bauxite b) Write the chemical formula of the major component of bauxite c) i) Name two major impurities in bauxite ii) Explain how the impurities in bauxite are removed d) Cryolite is used in the extraction of aluminium from bauxite. State its function f) Aluminium is a reactive metal yet utensils made of aluminium do not corrode easily. Explain this observation
Excess marble chips (calcium carbonate ) was put in a beaker containing 100cm3 of dilute hydrochloric acid. The beaker was then placed on a balance and the total loss in mass recorded after every two minutes as shown in the table below.
a) Why was there a loss in mass?
b) Calculate the average rate of loss in mass between: i) 0 and 2 minutes ii) 6 and 8 minutes iii) Explain the difference in the average rates of reaction in (b) (i) and (ii) above c) Write the equation for the reaction which takes place in the beaker d) State three ways in which the rate of the reaction above could be increased e) The solution in the beaker was evaporated to dryness what would happen if the open beaker and its contents were left in the laboratory overnight. f) Finally some water was added to the contents of the beaker. When aqueous sodium sulphate was added to the contents of the beaker, a white precipitate was formed. i) Identify the white precipitate ii) State one use of the substance identified in (f) (i) above
i) Identify the particles emitted in steps I and III
I II ii) Write the nuclear equation for the reaction which takes place in step V The table below give the percentages of a radioactive isotope of Bismuth that remains after decaying at different times. i) On the grid provided, plot a graph of the percentage of Bismuth remaining (Vertical axis) against time.
ii) Using the graph, determine the:
I. Half – life of the Bismuth isotope II. Original mass of the Bismuth isotope given that the mass that remained after 70 minutes was 0.16g d) Give one use of radioactive isotopes in medicine
a) The diagram below is a cross- section of a dry cell. Study it and answer the questions that follow.
i) On the diagram, show with a (+) sign the positive terminal
ii) Write the equation for the reaction in which electrons are produced
iii) The zinc can is lined with ammonium chloride and zinc chloride paste. iv) Give one advantage and one disadvantage of dry cells. b) The set – up below was used to (electrolyse roller lead (II) ionide.
i) State the observation that was made at the anode during the electrolysis.
Give a reason for your answer. ii) A current of 0.5 A was passed for two hours. Calculate the mass of lead that was deposited (Pb = 1F = 9,500C)
a) The chart below is an outline of part of the periodic table.
With the help of vertical and horizontal lines, indicate the direction of increasing metallic nature of the elements.
Which types of elements are represented in the shaded area? b) i) Element A is the same group of the periodic table as chlorine. Write the formula of the compound formed when A reacts with potassium metal. ii) What type of bonding exists in the compound formed in (b) (l) above? Give a reason for your answers. c) Starting with aqueous magnesium sulphate, describe how you would obtain a sample of magnesium oxide. d) Write two ionic equations to show that aluminum hydroxide is amphoteric
(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)
(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
(a) Candle wax is mainly a compound consisting of two elements.
Name the two elements (b) The set- up below was used to investigate the burning of a candle study it and answers the questions that follow
(i) What would happen to the burning candle if the pump was turned off? Give reasons
(ii) State and explain the changes in mass that are likely to occur in tube N by the end of the experiment (iii) Name two gases that come out through tube M (iv) Name another substance that could be used in the place of calcium oxide in tube N
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
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Air is less dense than carbon dioxide and so it enters the porous pot faster than carbon dioxide out of it. This sets up a higher pressure; in the pot and the level rises as shown:
Zinc metal and hydrochloric acid reacts according to the following equation Zn(s) + 2HCI (aq)→ ZnCI2 (aq) + H2 (g) 1.96 g of zinc were reacted with 100cm3of 0.2M hydrochloric acid (a) Determine the reagent that was in excess (b) Calculate the total volume of hydrogen gas was liberated S.T.P (Zn= 65.4 Molar gas volume = 22.4 litres at S.T.P) A fixed mass of a gas has a volume of 250cm3 at a temperature of 270C and 750mm Hg pressure. Calculate the volume the gas would occupy at 420C (2mks) (a) The diagram below shows a set-up that can be used to obtain nitrogen gas in an experiment. (i) Name liquid L (1mk) (ii) What observation would be made in tube K after heating for some time? (1mk) (iii) Write an equation for the reaction that took place in tube K. (1 mk) (iv) If 320 cm3 of ammonia gas reacted completely with the copper? Calculate: I Volume of nitrogen gas produced. (1mk) II the mass of copper oxide that reacted (3mks) (Cu = 63.5, O=16.O, one mole of gas occupies 24 liters at room temperature and pressure) (v) At the end of experiment the PH of the water in the beaker was found to be about ______________________ Explain (2mks) (b) In another experiment a gas jar containing ammonia was inverted over a burning splint. What observation would be made? (1mk) (c) Why is it advisable to obtain nitrogen from air instead ammonia? (1mk) 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) (a) The table below gives information about the major constituents of crude oil. Study it and answer the questions that follow. (i) Which one of the constituents or crude oil has molecules with the highest number of carbon atoms? (2mks) (ii) Name the process you would use to separate a mixture of petrol and diesel and explain how the separation takes place. (2mks) (iii) Explain why the constituent of crude oil and write its formula (1mk) (iv) Name one gas that is likely to be a constituent of crude oil and write its formula. (1mk) (b) What condition could cause a poisonous gas to be formed when Kerosene is burnt? Explain (2mks) (c) Give one use of bitumen (1mk) 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) In an experiment hydrogen chloride gas was prepared and reacted with aluminium turnings to form a solid q and gas R as shown in the diagram (i) Name: Liquid P : Solid Q (1mk) : Gas R (1mk) (ii) Name another substance that could serve the same purpose as the concentrated sulphuric acid. (1mk) (iii) Explain the following observation. When blue litmus paper was dipped into the water in the beaker at the end of the experiment it turned red. Explain why solid Q collects farther away from the heated aluminium (2mks) (b) (i) Write an equation for the reaction that takes place between ammonia gas and hydrogen gas (1mk) (ii) Calculate the mass of the product that would be formed when 2000cm3 of hydrogen chloride gas reacts completely with excess ammonia gas (H=1, O; N= 14.0, C1 = 35.5, one mole of gas occupied 24 litres at room temperature and pressure.) (3mks) The table below gives information on four elements by letters K, L, M and N. Study it and answer the questions that follow. The letters do not represent the actual symbols of the elements. a) Which two elements have two similar properties? Explain (2mks) |
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