KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
The column below was used do soften hard water
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A beekeeper found that when stung by a bee, application of a little solution of hydrogen carbonate helped to relieve the irritation from the affected area. Explain.
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The standard reduction potentials of two half –cells are:
Ag+(aq) + e → AG(s) ; E = 0.80V 2H2O (l) + 2e → H2 (g) + 2OH (aq); E1 = 0.83V Draw a labelled diagram of an electro chemical cell that can be constructed using the two half –cells
Hydrogen and oxygen can be obtained by electrolysis of acidified water.
Using equations for the reactions at the electrodes, explain why the volume of hydrogen obtained is twice that of oxygen. ​Related Chemistry Questions and Answers on Electrochemistry Form 4 Level
a) what is meant by molar heat of solution?
b) the lattice energy of sodium bromide and hydration energies of sodium and bromide ions are: 733,406 and 335 kJmol -1 respectively. i) Complete the energy cycle diagram below by inserting the values of ΔH1, ΔH2, and ΔH3
ii) Determine the molar heat of solution of solid sodium bromide.
When aluminium oxide was electrolysed, 1800kg of aluminium metal were obtained.
a) Write equation for the formation of aluminium metal b) Calculate the quantity of electricity in faradays used (Al=27)
Hardness of water may be removed by either boiling or addition of chemicals
a) write an equation to show how boiling removes hardness of water. b) name two chemicals that are used to remove hardness of water.
The scheme below shows some reaction sequence starting with solid N.
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(a) Define the standard enthalpy of formation of a substance
(b) Use the thermochemical equations below to answer the questions that follow.
(i) Name two types of heat changes represented by ΔH3
(ii) Draw an energy level diagram for the reaction represented by equation 1 (iii) Calculate the standard enthalpy of formation of ethane (iv) When a sample of ethane was burnt, the heat produced raised the temperature of 500g of water by 21. 5 K, (specific heat capacity of water = 4.2Jg-1K). Calculate the: I. Heat change for the reaction II. Mass of ethane was burnt. ( relative formula mass of ethane= 30)
The diagram below represents a set up that can be used to electrolyze aqueous copper (II) sulphate.
(a) (i) Describe how oxygen gas is produced during the electrolysis
(ii) Explain why copper electrodes are not suitable for this electrolysis (b) Impure copper is purified by an electrolytic process (i) Name one ore from which copper is obtained (ii) Write the equation for the reaction that occur at the cathode during the purification of copper (iii) In an experiment to electroplate a copper spoon with silver, a current of 0.5 A was passed for 18 minutes. Calculate the amount of silver deposited on the spoon (π = 96500 coulombs, Ag = 108) (iv) Give two reasons why some metals are electroplated
(a) Alkanes, alkenes and alkynes can be obtained from crude oil. Draw the structure of the second member of the alkyne homologous series.
(b) Study the flow chart below and answer the questions that follow
(i) State the conditions for the reaction in step 1 to occur
(ii) Identify substance II (iii) Give: I. One advantage of the continued use of substance such as J II The name of the process that takes place in step III III The name and the formula of substance K Name: Formula: (iv) The relative molecular mass of J is 16,800. Calculate the number of monomers that make up J. (c) The table below give the formula of four compounds L,M,N and P
Giving a reason in each case, select the letter which represents a compound that:
(i) Decolorizes bromine in the absence of UV light (ii) Gives effervescence when reacted with aqueous sodium carbonate
Draw the structural formula of:
Expected Response
a) (i) State the Le chatelier‟s principle.
(ii) Carbon (II) oxide gas reacts with steam according to the equation; CO(g) + H2O(g)→ H2(g)+ CO2(g) What would be the effect of increasing the pressure of the system at equilibrium? Explain. b) The table below gives the volumes of oxygen gas produced at different times when hydrogen peroxide decomposed in the presence of a catalyst.
(i) Name the catalyst used for this reaction
(ii) On the grid provided, draw the graph of volume of oxygen gas produced (vertical axis) against time. (iii) Using the graph, determine the rate of decomposition of hydrogen peroxide after 24 seconds. (iv) Give a reason why the total volume of oxygen gas produced after 50 seconds remains constant.
ANSWERS
(a)(i) When change is made to a system in equilibrium the System moves so as to oppose the change.
(ii)Pressure has no effect to equilibrium The moles/Volume/ molecules of gases is reactants and product are equal (iii) DH –ve ( negative) Since lowering of temperature moves to equilibrium to direction which heat is produced. Decrease in temperature favours exothermic reaction (b) (i) Manganese IV oxide
a) Biogas is a mixture of mainly carbon (IV) oxide and methane.
(i) Give a reason why biogas can be used as a fuel. (ii) Other than fractional distillation, describe a method that can be used to determine the percentage of methane in biogas. b) A sample of biogas contains 35.2% by mass of methane. A biogas cylinder contains 5.0 kg of the gas. Calculate the; (i) Number of moles of methane in the cylinder. (Molar mass of methane=16) (ii) Total volume of carbon (IV) oxide produced by the combustion of methane in the cylinder (Molar gas Volume=24.0 dm-3+ at room temperature and pressure). c) Carbon (Iv) oxide, methane, nitrogen (I) oxide and trichlorofluoromethane are green-house gases. (i) State one effect of an increased level of these gases to the environment. (ii) Give one source from which each of the following gases is released to the environment; I Nitrogen (i) oxide II Trichlorofluoromethane.
A certain mass of a metal E1 reacted with excess dilute hydrochloric acid at 25°C. The volume of hydrogen gas liberated was measured after every 30 seconds. The results were presented as shown in the graph below.
a) Name one piece of apparatus that may have been used to measure the volume of gas liberated. b) (i) On the same axis, sketch the curve that would be obtained if the experiment was repeated at 35°C. (ii) Explain the shape of your curve in b(i) above.
ANSWERS
(a)(i)Cryolite
(ii)Electrolysis (b)Good conductor Does not rust Malleable Light High M.P Does not corrode easily
Distinguished between a strong and a weak acid. Give examples.
In a closed system, aqueous iron (III) chloride reacts with sulphide gas as shown in the equation below.
2FeCl3(aq) + H2S(g) → 2FeCl2(aq) 2HCl(aq) + S(s) State and explain the observation that would be made if dilute hydrochloric acid is added to the system at equilibrium.
ANSWERS
(a)Amphoteric
(b)Lead (II), Zinc and Aluminium
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