KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
(a) Describe the process by which Nitrogen is obtained from air on a large scale.
(b) Study the flow chart below and answer the questions that follow.
(i) Identify gas J.
(ii) Using oxidation numbers, show that ammonia is the reducing agent in step (VI) (iii) Write the equation for the reaction that occurs in step (V). (iv) Give one use of ammonium nitrate. (c) The table below shows the observations made when aqueous ammonia was added to cations of elements E, F and G until in excess.
(i) Select the cation that is likely to be Zn2+
(ii) Given that the formula of the cation of element E is E 2+ , write the ionic equation for the reaction between E2+(aq) and aqueous ammonia.
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Use the information in the table below to answer the questions that follow. The letters do not represent the actual symbols of the elements.
(a) Give reasons why the melting point of:
(i) S is higher than that of R; (ii) V is lower than that of U. (b) How does the reactivity of W with Chlorine compare with that of R with chlorine? Explain. (c) Write an equation for the reaction between T and excess oxygen. (d) When 1.15g of R were reacted with water, 600cm3 of gas was produced. Determine the relative atomic mass of R. (Molar gas volume = 24 000 cm3). (e) Give one use of element V.
(a) What is meant by rate of reaction. (1 mark)
(b) In the space provided, sketch the diagram of a set-up that can be used to determine the rate of reaction between manganese(IV) oxide and hydrogen peroxide. (3 marks)
(e) A student placed a small amount of liquid bromine at the bottom of a sealed gas jar of air as shown in Figure 4.
(i) Describe what will be observed: (1 mark)
I. after two minutes . II. after 30 minutes
(ii) Use the Kinetic theory to explain the observations: (2 marks)
I. after 2 minutes . II. after 30 minutes
(d) Some plants have seeds that contain vegetable oil.
(a) What is meant by standard electrode potential of a an element? (1 mark)
(b) use the standard electrode potentials given below to answer the questions that follow.
(i) State whether acidified MnO4- can oxidise M2+. Give a reason. (2 marks) (ii) Select two half-cells which when combined will give the highest e.m.f. (1 mark) (iii) Write the cell representation for the cell formed in b (ii). (I mark) (iv) Calculate the E0 value for the cell formed in b (iii). (2 marks) (c) A mass of 1.24g of a divalent metal was deposited when a current of 6A was passed through a solution of the metal sulphate for 12 minutes. Determine the relative atomic mass of the metal.
(1 Faraday = 96,500 C mol-1 (3 marks)
(d) State two applications of electrolysis. (I mark)
(a) What ¡s meant by molar heat of neutralisation? (1 mark)
(b) In an experiment to determine the molar heat of neutralisation, 50 cm3 of 1M hydrochloric acid was neutralised by adding 10 cm3 portions of dilute sodium hydroxide. During the experiment, the data in Table 1 was obtained.
(iii) Determine from the graph the: I. volume of sodium hydroxide which completely neutralises 50 cm3 of 1M hydrochloric acid. (1 mark) II. change in temperature,△T, when complete neutralisation occurred. (1 mark) (iv) Calculate: I. the heat change, △H when complete neutralisation occurred. (Specific heat capacity = 4.2 Jg-1K-1, density of solution 1.0 gcm-3) (2 marks) II. molar heat of neutralisation of hydrochloric acid with sodium hydroxide. (1 mark) (v) How would the value of molar heat differ if 50 cm3 of 1M ethanoic acid was used instead of 1M hydrochloric acid? Give a reason. (2 marks)
When a student was stung by a nettle plant, a teacher applied an aqueous solution of ammonia to the affected area of the skin and the
student was relieved of pain. Explain.
ANSWERS
A mixture contains ammonium chloride, copper (II) oxide and sodium chloride. Describe how each of the substances can be obtained form the mixture.
ANSWERS
Describe an experimental procedure that can be used to extract oil from nut seeds.
ANSWERS
Crush grind using a pestle and mortar, add suitable solvent of propanone ethanol alcohol and stir to dissolve oil. Filter the mixture to obtain a solution of the oil. Leave the solution in the sun for propanone to evaporate leaving the oil.
Hydrogen sulphide is a highly toxic and flammable gas. It is normally prepared in a fume chamber.
(a) Name two reagents that can be used to prepare hydrogen sulphide in the laboratory. (b) One of the uses of hydrogen sulphide is to produce sulphur as shown in the following equation: 2H2S(g) + S02 (g) -> 3S(s) + 2H20(1) Identify the reducing agent in this reaction and give a reason for your answer. (c) Other than production of sulphuric (VI) acid, state one commercial use of sulphur.
ANSWERS
(a)Iron (II) sulphide or conc sulphide / copper sulphide (Accp formula: Fes/ HCl)
Hydrochloric acid or lead (II) sulphide/ HNO3 (b)Hydrogen sulphide The sulphur changes from -2 to zero/ (it reduces SO2 to S) i.e. +4 to 0 / sulphur lost e’s in the H2S to form sulphur (c)Vulcanization of rubber Manufacture of sulphur drugs Manufacture of gun powder/ match sticks / explosives/ fungicides
Charcoal is a fuel that is commonly used for cooking. When it burns it forms two oxides.
(a) Name the two oxides. (b) State one use of the two oxides.
ANSWERS
(a)Carbon (IV) oxide /CO2/ carbon dioxide
Carbon (II) oxide/ CO/ carbon monoxide (b)Fire extinguisher/ photosynthesis Refrigeration Solvay process Fizzy drinks Food preservation Extraction of metals Manufacture of methanol Manufacture of fuel (water, gas)
Describe how a solid sample of potassium sulphate can be prepared starting with 200cm3of 2M potassium hydroxide.
Given the following substances: wood ash, lemon juice and sodium chloride.
(a) Name one commercial indicator that can be used to show whether wood ash, lemon juice and sodium chloride are acidic, basic or neutral. (b) Classify the substances in 15(a) above as acids, bases or neutral.
ANSWERS
(a) Litmus
Phenolphthalein indicator (b) Wood ash- Basic Lemon Juice - acidic Sodium Chloride- neutral
The set-up below was used to collect a dry sample of a gas
Give two reasons why the set-up cannot be used to collect carbon (IV) oxide gas.
ANSWERS
Draw and name the isomers of pentane.
60 cm3 of oxygen gas diffused through a porous partition in 50 seconds. How long would it take 60cm3 of sulphur (IV) oxide gas to diffuse through the same partition under the same conditions? (S = 32.0, 0 = 16.0)
In an experiment on rates of reaction, potassium carbonate was reacted with dilute sulphuric (VI) acid.
(a) What would be the effect of an increase in the concentration of the acid on the rate of the reaction? (b) Explain why the rate of reaction is found to increase with temperature.
ANSWERS
(a)The rate of reaction increases. This is because when the concentration is high: the number of collisions between particles is also high hence reacts faster,
(b)Increase in temperature results in increase in the kinetic energy of the particles. This makes particles move faster and collide frequently leading to faster rate of reaction.
A water trough, aqueous sodium hydroxide, burning candle, watch class and a graduated gas jar were used in an experimental set up to determine the percentage of active part of air. Draw a labeled diagram of the set up at the end of the experiment.
A compound whose general formula is M(OH)3 reacts as shown by the equation below.
(a) What name is given to compounds which behave like M(OH) 3 in the two reactions.
(b) Name two elements whose hydroxides behave like that of M.
ANSWERS
(a) Amphoteric
(b)Lead, Zinc and Aluminium
The atomic number of sulphur is 16. Write the electron arrangement of sulphur in the following:
(a) Zinc occurs mainly as zinc blende. Name one other ore from which Zinc can be extracted. (1 mark)
(b) The flow chart in Figure 2 shows the various stages in the extraction of zinc metal. Study it and answer the questions that follow.
(c) Explain the observations made when zinc metal is added to hot sodium hydroxide. (2 marks)
Figure 3 is a flow chart that shows the process that occurs in the manufacture of nitric (V) acid.
(a) Name substance P, Q, R and S.
To obtain substance R, ammonia is heated at 9000C in the presence of air and a catalyst.
The product is then cooled in air.
(e) When ammonia ¡s reacted with nitric(V) acid, it produces a nitrogenous fertiliser.
(a) Explain the following observations:
(b) A sample of water is suspected to contain aluminium ions (AI3+) . Describe a laboratory experiment that can be carried out to show that AI3+ ions are present in the water sample. (3 marks) (c) In an experiment to determine the number of moles of water of crystallisation of a hydrated compound, Na2S04. X H2O, 5g of the compound were heated strongly to a constant mass.
1.
(a) Alkanes are said to be saturated hydrocarbons.
(b) When the alkane, hexane, is heated to high temperature, one of the products is ethene.
Related Chemistry Questions and Answers on Organic Chemistry II Form 3 Level
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Expected Response
​volumetric flask
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