KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
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
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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) 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 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
Expected response
Pentane: It is non poler and will not react with sodium Hydroxide solution which is an ionic compound.
Name the organic compound formed when CH3CH2CH2CH2CH2OH is reacted with concentrate sulphuric acid at 170°C
answer
When X cm3 of a solution of 0.5m magnesium carbonate was 8.4g.
a) Write the ionic equation for the reaction that took place b) Calculate the value of X. (C = 12.0, Mg 24.0; 016.0
a) What is the name given to the smallest repeating unit of a polymer.
b) Draw the structure of the smallest repeating unit of a polyvinyl chloride
Explain why a high temperature is required for nitrogen of react with oxygen
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Nitrogen forms many compounds in which its oxidation state varies.
a) What is meant by oxidation state? b) What is the oxidation state of nitrogen in Mg3N2
ANSWERS
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In an experiment, 2.4g of sulphur was obtained by reacting hydrogen sulphide and chorine as shown by the equation below: H2S(g) + Cl2(g) → S(s) + 2HCl(g) (a) Which of the reactants acts as a reducing agent in the above reaction? Explain. (1 mk) (b) Given that the yield of sulphur in the above reaction is 75%, calculate the number Of moles of H2S(g) used in the reaction (S=32.0)
expected response
a)
i) Iron (II) Suphide ii) Hydrogen Sulphide
b) Darker paper soaked in lead acetate
Chlorine and iodine are elements in the same group in the periodic table. Chlorine gas is yellow white aqueous, iodine; I2(aq) is brown. a) What observation would be made if chlorine gas is bubbled through aqueous sodium iodide? Explain using and ionic equation. (2mks) b) Under certain conditions chlorine and iodine react to give iodine chloride, ICl3(s)- What type of bonding would you expect to exist in iodine trichloride? Explain (1mk)
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.
expected response
I, production of carbon dioxide or carbon is oxidized to its highest oxidation number/carbon dioxide cannot burn further or carbon dioxide cannot burn further or carbon monoxide can burn further
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The graph below shows the behaviour of a fixed mass of a gas at constant temperature.
a) What is the relationship between the volume and the pressure of the gas?
b) 3 litres of oxygen gas at one atmosphere pressure were compressed to two atmospheres at constant temperature. Calculate the volume occupied by the oxygen gas
a) State the observation made when excess pentane is reacted with bromine gas
b) Name the compound formed in (a) above.
answers
The set – up below was used to prepare hydrogen chloride a gas and react it with iron powder. Study it and answer the questions that follow.
At the end of the reaction, the iron powder turned into a light green solid.
a) Identity the light green solid. b) At the beginning of the experiment, the Ph of the solution in container L was about 14.. At the end, the pH was found to be 2. Explain
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Oleum (H2S2O7) is an intermediate product in the industrial manufacture of sulphuric acid
(a) How is oleum converted into sulphuric acid? (b) Give one use of sulphuric acid
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