KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
a) The diagram below shows some processes that take place during the industrial manufacture of sulphuric acid.
(i) Write the equation for the reaction in which sulphur dioxide gas is produced.
(ii) Why is it necessary to keep the gases pure and dry ? (iii) Describe the process that takes place in chamber G. (iv) Name the gases that escape into the environment. (v) State and explain the harmful effect on the environment of one of the gases named in (iv) above (vi) Give one reason why it is necessary to use a pressure of 2-3 atmospheres and not more. b) (i) Complete the table below to show the observations made when concentrated sulphuric acid is added to the substances shown.
(ii) Give reasons for the observations made using:
I iron fillings II Crystals of white sugar. (c) Name one fertilizer made from sulphuric acid. (d) Suggest a reason why BaSO4(a pigment made from sulphuric acid) would be suitable in making paint for cars.
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a) Distinguish between isotopes and allotropes.
b) The chart below is part of the periodic table. Study it and answer the questions that follow.(The letters are not the actual symbols of the elements).
i) Select the element in period three which has the shortest atomic radius. Give a reason for you answer.
ii) Element F has the electronic structure, 2.8.18.4 on the chart above, indicate the position of element F. iii) State one use of the elements of which E is a member. iv) Write an equation to show the action of heat on the nitrate of element C. c) When 3 litres of chlorine gas were completely reacted with element D, 11.875g of the product were formed. Determine the relative atomic mass of element D. (Atomic mass of chlorine = 35.5; molar gas volume = 24litres)
a) In an experiment to determine the molar heat of reaction when magnesium displaces copper ,0.15g of magnesium powder were added to 25.0cm3 of 2.0M copper (II) chloride solution. The temperature of copper (II) chloride solution was 25°C.While that of the mixture was 43°C.
i) Other than increase in temperature, state and explain the observations which were made during the reaction. ii) Calculate the heat change during the reaction (specific heat capacity of the solution = 4.2jg-1k-1and the density of the solution = 1g/cm3 iii) Determine the molar heat of displacement of copper by magnesium.(Mg=24.0). iv) Write the ionic equation for the reaction. v) Sketch an energy level diagram for the reaction. b) Use the reduction potentials given below to explain why a solution containing copper ions should not be stored in a container made of zinc.
a) What is an electrolyte?
b) State how the following substances conduct electricity. i) Molten calcium chloride ii) Graphite. c) The diagram below shows a set up that was used to electrolyse aqueous magnesium sulphate.
i) On the diagram above, using an arrow, show the direction of flow of electrons.
ii) Identify the syringe in which hydrogen gas would be collected. Explain d) Explain why the concentration of magnesium sulphate was found to have increased at the end of the experiment. e) During the electrolysis, a current of 0.72A was passed through the electrolyte for 15 munities. Calculate the volume of gas produced at the anode.(1 Faraday = 96 500 coulombs; molar gas volume is 24000cm3 at room temperature).
(a) Below is a simplified diagram of the Downs Cell used for the manufacture of sodium.
Study it and answer the questions that follow
(i) What material is the anode made of? Give a reason
(ii) What precaution is taken to prevent chlorine and sodium from re- combination? (iii) Write an ionic equation for the reaction in which chlorine gas is formed (b) In the Downs process, (used for manufacture of sodium), a certain salt is added to lower the melting point of sodium chloride from about 800°C to about 600°C. (i) Name the salt that is added (ii) State why it is necessary to lower the temperature (c) Explain why aqueous sodium chloride is not suitable as an electrolyte for the manufacture of sodium in the Downs process (d) Sodium metal reacts with air to form two oxide. Give the formulae of two oxides
(a) The list below shows the formulae of some organic compounds. Use it to answer the questions that follow.
(i) Select two compounds whichI are not hydrocarbons II Belong to the same homologous series
(ii) Identify the compound that is likely to undergo polymerization. Give a reason for your answer. a. The structures below represents two cleansing agents: R – COO- Na+ R – OSO3- Na+ In the table below, give one advantage and one disadvantage of using each one of them
b. Under certain, ethanoic acid ( C2H4O2) and ethanol (C2H5OH) react to form a sweet smelling compound.
(i) What is the general name of compound to which the sweet smelling compound belong? (ii) Write the formula of the sweet smelling compound (iii) Give one use of ethanoic acid other the formation of the sweet smelling compounds (iv) Write the equation for the reaction dilute ethanoic acid and solid potassium carbonate c. Fibres are either synthetic or natural. Give one: (i) Example of a natural fibre (ii) Advantage of synthetic fibres have over natural fibres
In an experiment, a piece of magnesium ribbon was cleaned with steel wool. 2.4 g of the clean magnesium ribbon was placed in a crucible and completely burnt in oxygen. After cooling, the product weighed 4.0 g
(a) Explain why it was necessary to clean the magnesium ribbon (b) What observation was made in the crucible after burning (c) Why was there an increase in mass? (d) Write the equation for the reaction which took place in the crucible (e) The product in the crucible was shaken with water and filtered. Explain the observation which was made when blue and red litmus papers were dropped into the filtrate.
(a) An atom Q can be represented as
What does the number 52 represent?
(b) Study the information in the table below and answer the equations that follow (Letters are not the actual symbols of the elements)
(i) Write the formula of the compound formed when N reacts with P. (atomic numbers are N = 20; P = 17)
(ii) Identify the elements which belong to the third period of the periodic table. Explain (iii) Which of the element identified in b (ii) above comes first in the third period? Explain (iv) Select two elements which are non- metals (c) The table below gives some properties of substances I, II, III, and IV. Study it and answer the questions that follow
(i) What type of bonding exists in substances I and II
I II (ii) Which substances is likely to be sulphur? Explain
(a) The table below shows the standard reduction potentials for four half- cells.
Study it and answer the questions that follow. (Letters are not the actual symbols of the elements)
(i) Identify the strongest reducing agent
(ii) Write the equation for the reaction which takes place when solid G is added to a solution containing H2+ ions (iii) Calculate the Eθ value for the reaction in (ii) above (b) The diagram below shows the apparatus that can be used to electrolyze acidified water to obtain hydrogen and oxygen gases. Study it and answer the questions that follow
(i) Identify the electrode at which oxidation takes place
(ii) Give a reason why it is necessary to acidify the water (iii) Explain why hydrochloric acid is not used to acidify the water (c) During electrolysis of aqueous copper (II) sulphate, 144750 coulombs of electricity were used. Calculate the mass of copper metal that was obtained Cu = 64 ; 1 Faraday = 96500 coulombs)
(a) Name one raw material which sodium hydroxide is manufactured
(b) Sodium hydroxide pellets were accidentally mixed with sodium chloride 17.6 g of the mixture were dissolved in water to make one litre of solution. 100 cm3 of the mixture were dissolved in water to make one litre solution. 100cm3 of the solution was neutralized by 40cm3 of 0.M sulphuric acid (i) Write an equation for the reaction that took place (ii) Calculate the: (i) Number of moles of the substance that reacted with sulphuric acid (ii) Number of moles of the substances that would react with sulphuric acid in the one litre of solution (iii) Mass of the unreacted substances in one litre of solution (H = 1,0 ; Na = 23.0 ; Cl= 35.5 ; 0= 16.0) (c) The diagram below shows an incomplete set-up used to prepare and collect ammonia gas
(i) Name solid M
(ii) Complete the diagram to show how a dry sample of ammonia gas can be collected (d) In an experiment, excess ammonia gas passed over heated copper (II) oxide on a combustion tube. (i) State the observation that was made in the combustion tube at the end of the experiment (ii) What property of ammonia is shown in the above reaction (iii) Name one use of ammonia
(a) The diagram below shows spots of pure substance A,B, and C on a chromatography paper. Spot D is that of a mixture
After development, A, B and C were found to have moved 8cm, 3cm and 6 cm respectively. D has separated into two spots which had moved 6cm and 8 cm
(i) On the diagram I Label the baseline ( origin) II Show the positions of all the spots after development (ii) Identify the substances present in the mixture D (b) Describe how solid ammonium chloride can be separated fro a solid mixture of ammonium chloride and anhydrous calcium chloride (c) The table shows liquids that are miscible and those that are immiscible
Use the information given to answer the questions that follow
(i) Name the method that can be used to separate L1 and L3 from a mixture of two (ii) Describe how a mixture of L2 and L4 can be separated
ANSWERS
(ii) A and C b)Since NH4CL4 sublimes but CaCl2 does not; sublimation process would do. Heat the mixture. Ammonium chloride sublimates into vapour and condenses on the cooler part of the heating tube. Calcium chloride will remain on the bottom of the heating tube. c)i)Fractional distillation ii)Separating funnel method Since the tow liquids are immiscible, pour both the liquids in a separating funnel and allow to settle, the denser liquid will settle down and the less dense will form a second layer on top. Open the tape and run out the liquid in the bottom layer leaving the liquid in the second layer in the funnel.
(a) The graph below shows the solubility of sulphur dioxide gas at different temperatures. Use the following in it to answer the questions that follow.
(i) From the graph determine: I The lowest temperature at which 1,000cm3 of solution would contain 116g of sulphur dioxide. II The maximum mass of sulphur dioxide that would dissolve in 15 litres of solution at 100C (ii) Sodium hydroxide reacts with sulphur trioxide according to the following equation. Using the information in the graph determine the volume of 2M sodium hydroxide required to completely neutralize on one litre of saturated sulphur dioxide solution 230C. (S=32.0; O; O = 16.0) (3mks) (b) Study the flow chart below and answer the questions that follow. Write equation for the reaction taking place at: I The roasting furnace (1mk) II The absorption tower (1mk) III The diluter (1mk) (ii) The reaction taking place in chamber K is I Explain why it is necessary to use excess air in chamber K II Name another substance used in chamber K (c) Study the scheme given below and answer the questions that follow: (i) Name the reagents used in: Step I……………… (1mk) Step II……………… (1mk) Step IV…………… (1mk) (ii) Write an equation for the complete combustion of CH = CH (1mk) Explain one disadvantage of the continued use of items made from the compound formed in step III (2mks)
Study the table below and answer the questions that follow:
a) Complete the table by filling in this missing atomic numbers and atomic mass. (2mks) b) Write the electron arrangement for the following ions (2mks) Ca+ P3+ c) What is the melting point of hydrogen in degrees Kelvin? (1mk) d) Which of the allotropes of phosphorous ha a higher density? Explain (2mks) e) The mass numbers of three isotopes of magnesium are 24, 25 and 26. What is the mass number of the most abundant isotope of magnesium? Explain (2mks) f) Give the formula of the compound formed between aluminium and carbon.(1mks) g) Explain the difference in the melting points of magnesium and sodium.(2mks) a) Give the name of each of the processes described below which takes place when salts are exposed to air for sometime. i) Anhydrous copper sulphate becomes wet (1mk) ii) Magnesium chloride forms an aqueous solution (1mk) iii) Fresh crystals of sodium carbonate, Na2CO3. 10H2O (1mk) b) Write the formula of the complex ion formed in each of the reactions described below. (i) Zinc metal dissolves in hot alkaline solution (1mk) (ii) Copper hydroxide dissolves in excess ammonia solution. (1 mk) (c) A hydrated salt has the following composition by mass. Iron 20.2% Oxygen 23.0%, sulphur 11.5%, water 45.3 %. Its relative formula mass is 278. (i) Determine the formula of the hydrated salt.. (3mks) (Fe=56, S=32; O = 16, H =1) (ii) 6.95gm of the hydrates salt were dissolved in distilled water and the total volume made to 250 cm3 of solution. Calculate the concentration of the salt solution in moles per litre.
a) Study the table below and answer the questions that follow
i) Which of the compounds is a solid at 10.00C? Explain (1mk) ii) Choose two compounds which are members of the same homologous series and explain the difference in their melting points. (3mks) iii) The compound C3H8O is an alcohol. How does its solubility in water differ from the solubility of C5H12 in water? Explain. (2mks) b) Complete combustion of one mole of a hydrocarbon produced four moles of carbon dioxide and four moles of water only. i) Write formula of the hydrocarbon (1mk) ii) Write the equation for the combustion reaction: (1mk) c) In a reaction, an alcohol J was converted to a hex- 1 – ene. i) Give the structural formula of the alcohol J ii) Name the reagent and conditions necessary for the reaction in c (i) above d) Compound K reacts with sodium hydroxide as shown below? (1mk) i) What type of reaction is represented by the equation above? (1mk) ii) To what class of organic compounds does K belong? (1mk)
The extraction of aluminium from it s ore takes place in two stages, purification stage and electrolysis stage. The diagram below shows the set – up for the electrolysis stage
a)
i) Name the ore from which aluminium extracted. (1mk) ii) Name one impurity, which is removed at the purification stage.(1mk) b) i) Label on the diagram each of the following i) Anode ii) Cathode iii) Region containing the electrolyte. ii) The melting point aluminium oxide is 20540C, but electrolysis is carried out between 800 – 9000C. i) Why is the electrolysis not carried out at 20540C (1mk) ii) What is done lower the temperatures? (1mk) iii) The aluminium which is produced is tapped off as aliquid. What does this suggest about it smelting point? (1mk) c) A typical electrolysis cell uses current of 40,000 amperes.Calulate the mass (in kilograms) of aluminium produced in one hour) (3mks)
a) The diagram below shows incomplete set – up of the laboratory and preparation collection of chlorine gas. Study it and answer the questions that follow.
i) Complete the set – up to show how dry chloride gas may be collected.
ii) The equation for the redox reaction that takes place is
Explain, using oxidation numbers, which species is reduced (2mks)
iii) What is the purpose of water in flask L? (1mk) b) Study the diagram below and answer the questions that follow.
When some hydrogen chlorides gas is allowed into water and the mixture stirred, the bulb lights and gases X and Y are formed.
i) Name: Gas X Gas Y ii) Explain why the bulb does not light before the hydrogen chloride gas is let into water. (2mks) iii) Explain using equations why the volume of gas X is less than that of gas (2mks)
Sodium thiosulphate solution reacts with dilute hydrochloric acid according to the following equation.
In an experiment to study how the rate of reaction varies withconcentration, 10cm3 of 0.4M sodium thiosulphate was mixed with 10cm3. Of 2M hydrochloric acid in a flask. The flask was placed in a white paper marked with across X.The time taken for the cross X become invisible when viewed from above was noted and recorded in the table below. The experiment was repeated three times as the temperature using the volumes in the table and the results recorded as shown in the table below. a) i) On the grid below, plot a graph of the volume of thiosulphate (Vertical axis) against time taken for the cross (X) to become invisible) ii) From the graph determine how long it would take for the cross to become invisible if the experiment was done. (3mks) i) Using 6cm3 of the 0.4M thiosulphate (1mk) ii) Using 6cm3 of 0.2M thiosulphate solution (1mk) b) i) Using values for experiment I.Calculate i) Moles of thiosulphate used (1mk) ii) Moles of hydrochloric acid used (1mk) ii) Explain which of the two reactants in experiment I controlled the rate of the reaction? Explain (1mk) c) Give two precautions which should be taken in experiment I controlled the rate of the reaction? Explain (2mk)
(a) Brine usually contains soluble calcium and magnesium salts. Explain how sodium carbonate is used to purify brine.
b) The diagram below represents a diaphragm cell used to electrolysed pure brine
i) Write the equations for the reactions that take place at
I Cathode II Anode ii) Name: I Product at U II Another material that can be used instead of titanium III The impurity present in the product at U iii) State two functions of the diagram c) Give one industrial use of the product at U.
a) Crude oil is a source of many compounds that contain carbon and hydrogen only.
(i) Name the processes used to separate the components of crude oil (ii) On what two physical properties of the above components does the separation depend? b) Under certain conditions, hexane can be converted to two products. The formula of one of the products is C3H3 (i) Write the formula of the other product (ii) Describe a simple chemical reaction to show the difference between the two products formed in (b) above. c) Ethane, C2H2 is another compound found in crude oil. One mole of ethane was reacted with one mole of hydrogen chloride gas and a product p1 and was formed. P1 was then reacted with excess hydrogen gas to form p2. Draw the structures p1 and p2. d) The set-up below was used to prepare and collect ethane gas. Study it and answer the questions that follow.
(i) Name the substance T
(ii) Give the property of ethane that allows it to be collected as shown in the set up. e) One of the reactions undergone by ethane is addition polymerization. Give the name of the polymer and one disadvantage of the polymer it forms. (2 marks) Name the polymer. Disadvantage of the polymer
The flow chart below shows some reactions starting with lead (II) nitrate. Study it and answer the questions that follow.
(i) State the condition necessary in step 1.
(ii) Identify: I Reagent K II Gas Q III Acidic products S and R (iii) Write: I The formula of the complex ion formed instep 3. II The equation of the reaction in step 4 b) The use of materials made of lead in roofing and in water pipes is being discouraged State: (i) Two reasons why these materials have been used in the past. (ii) One reason why their use is being discouraged c) (i) The reaction between lead (II) nitrate and concentrated sulphuric acid starts but stops immediately. Explain
a) at 250°C , 50g of potassium were added to 100gm of water to make a saturated solution. What is meant by a saturated solution?
b) The table below gives the solubilities of potassium nitrate at different temperatures.
(i) Plot graph of the solubility of potassium nitrate (vertical axis) against temperature
(ii) Using the graph: I Determine the solubility of potassium nitrate at 15°C II Determine the mass of potassium nitrate that remained undissolved given that 80g of potassium nitrate were added to 100cm3 of water and warmed to 40°C. c) Determine the molar concentration of potassium nitrate at 15°C (Assume there is no change in density of water at this temperature) (K = 39. 0; N= 14.0; O = 16.0)
a) The diagram below illustrates how Sulphur/extracted by the Frisch process.
Label the pipe through which superheated water is pumped in
b. The equation below shows the oxidation of sulphur dioxide to sulphur trioxide in the contact process.
(i) Name one catalyst for this reaction
(ii) State and explain the effect on the yield of sulphur trioxide when: I The temperature increased II The amount of oxygen is increased (iii) Describe how sulphur trioxide is converted to sulphuric acid in the contact process. (c) State two disadvantages of having sulphur dioxide in the environment (d) Ammonia sulphate is a fertilizer produced by passing ammonia gas into concentrated sulphuric acid. (i) Write the equation for the reaction (ii) Calculate the mass in Kg of sulphuric acid required to produce 25kg of the fertilizer (S = 32.0; O= 16.0; N = 1.0)
a) The set-up below was used to collect gas F, produced by the reaction between water and calcium metal.
(i) Name gas F
(ii) At the end of the experiment, the solution in the beaker was found to be a weak base. Explain why the solution is a weak base. (iii) Give one laboratory use of the solution formed in a beaker. (b) The scheme below shows some reactions starting with calcium oxide. Study it and answer the questions that follow.
(i) Name the reagents used in steps 2 and 4
Step 2 ………. Step 4 ………. (ii) write an equation for the reaction in step 3. (iii) Describe how a solid sample of anhydrous calcium sulphate is obtained in Step 5
a) The table below shows properties of chlorine, bromine and iodine.
Complete the table by giving the missing information in (i),(ii) and (iii)
b) Chlorine gas is prepared by reacting concentrated hydrochloric acids with manganese (iv) oxide. i) Write the equation for reaction between concentrated hydrochloric acid and manganese (iv) oxide. ii) What is the role of manganese (Iv) oxide in this reaction c) i) Iron (II) chloride reacts with chlorine gas to form substance E. Identify substance E ii) During the reaction in c(i) above,6.30g of iron chloride were converted to 8.06 of substance E. Calculate the volume of chlorine used.(Cl = 35.5, Molar gas volume at room temperature = 24000cm3, Fe =56 ) d) Draw and name the structure of the compound formed when excess chlorine gas is reacted with ethane gas. e) Give the industrial use of chlorine |
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