KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
When solid magnesium carbonate was added to a solution of hydrogen chloride in methylbenzene, there was no apparent reaction. On addition of water to the resulting mixture, there was vigorous effervescence. Explain these observations
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One of the fuels associated with crude oil is natural gas. Name the main constituent of natural gas and write an equation for its complete combustion
Name: Equation:
When excess carbon monoxide gas was passed over heated lead (II) oxide in combustion tube, lead (II) oxide was reduced
(a) Write an equation for the reaction, which took place (b) What observation was made in the combustion tube when the reaction was complete? (c) Name another gas, which could be used to reduce lead (II) oxide
Expected Response
(a) Pb(s) + CO(g) →Pb(s) + CO2(g)
(b) Silvery white or grey metal/ shiny grey metal (c) Hydrogen gas / ammonia
Compound L reacts with hydrogen bromide gas to give another compound whose structure is
(a) Give the structural formula and name of compound L
(b) Write an equation for the reaction, which takes place between ethane and excess chlorine gas
State and explain one disadvantages of using hard water in boilers
Expected Response
On boiling hard water deposits CaCO3 which forma fur/ scales in the boiler. This reduces conductivity
Graphite is one of the allotropes of carbon.
(a) Name one other element which exhibits allotropy. (b) Explain why graphite is used in the making of pencil leads.
ANSWERS
(a) Sulphur or phosphorus.
(b) Carbon atoms in graphite are arranged in layers of hexagons which are held by weak van der waal forces. The layers slide over each other when some force is applied on them; hence suitable in making pencil leads.
Describe how the PH of anti-acid (Actal) powder can be determined in the laboratory
ANSWERS
50kg of ammonium sulphate (NH4)2SO4and 30kg of urea CO(NH2)2 fertilizers were applied in two equal sizes of plots A and B to enrich their nitrogen content.Show by working, which plot was more enriched with nitrogen. (N =14;S = 32; O = 16; C = 12; H = 1)
Under certain conditions, chlorine gas reacts with sodium hydroxide to form sodium hypochlorite.
(a) Name the conditions under which sodium hydroxide reacts with chlorine to form sodium hypochlorite. (b) State two uses of sodium hypochlorite.
ANSWERS
(a) Cold and dilute sodium hydroxide.
(b) Used in sterilizing of water. Used as a bleaching agent.
The set up below was used to prepare a gas and study some of its properties. Study it and answer the questions that follow:
(a) State and explain the observations made in the:
(i) tube labelled A; (ii) beaker labelled B. (b) State one precaution that should be taken when carrying out this experiment.
ANSWERS
(a) (i) Black solid is deposited.
(ii) The indicator turns red. (b) The experiment should be done in fume chamber or in open air.
Ethanoic acid and ethanol react as shown in the equation below:
Other than warming, how would the state of equilibrium be established within a short time?
Soap dissolves in water according to the equation below;
NaSt(aq) —> Na+(aq) + St- where St- is the stearate ion. (a) Write the formula of the scum formed when soap is used in hard water. (b) Write the ionic equation for the reaction that occurs when sodium carbonate is used to remove hardness in water.
Two organic compounds P and Q decolourise acidified potassium manganate (VII) solution but only P reacts with sodium metal to give a colourless gas. Which homologous series does compound P belong? Give a reason.
ANSWERS
P is in alkanol R - OH. The alkanol reacts with sodium metal to produce the colourless gas.
Distinguish between the terms deliquescent and efflorescent as used in chemistry
ANSWERS
Sodium hydroxide can be prepared by the following methods; I and II.
(a) Name the precaution that needs to be taken in method I.
(b) Give the name of process A. (c) Give one use of sodium hydroxide,
ANSWERS
(a) Small piece of sodium metal (pea size) with a lot of water.
Perform the experiment wearing goggles. (b) Electrolysis. (c) Manufacture of soap.
Exhaust fumes of some cars contain carbon(II)oxide and other gases.
(a) Explain how carbon (II) oxide is formed in the internal combustion engines. (b) Name two gases other than carbon (II) oxide that are contained in exhaust fumes and are pollutants.
ANSWERS
(a) Carbon (II) oxide is formed in the internal combustion engines when fuel burns under limited oxygen.
(b) Pollutant gas - Carbon (IV) oxide, Nitrogen (1V) oxide and Sulphur (IV) oxide.
During a class experiment, chlorine gas was bubbled into a solution of potassium iodide.
(a) State the observations made. (b) Using an ionic equation, explain why the reaction is redox .
State two reasons why hydrogen is not commonly used as a fuel.
ANSWERS
(a) What is meant by a strong acid?
(b) In an experiment 40cm3 of 0.5M hydrochloric acid was reacted with excess sodium carbonate and the volume of carbon (IV) oxide produced recorded with time. In another experiment, the same volume and concentration of ethanoic acid was also reacted with excess sodium carbonate and the volume of carbon (IV) oxide produced recorded with time. On the grid below, sketch and label the curves if the volumes of carbon (IV) oxide were plotted against time.
When lead(II) nitrate is heated, one of the products is a brown gas.
(a) Write the equation of the reaction that occurs . (b) If 0.290dm3 of the brown gas was produced, calculate the mass of the lead(II) nitrate that was heated. (R .F.M of lead (II) nitrate = 331; Molar gas volume = 24dm3 ).
A certain mass of gas occupies 0.15dm3 at 293K and 98,648.5Pa. Calculate its Volume at 101,325Pa and 273K.
The diagram below represents part of the periodic table. Use it to answer the questions that follow.
a) Write the electronic arrangement for the stable ion formed by W.
(b) Write an equation for the reaction between V and Q. (c) How do the ionization energies of the elements M and T compare? Explain.
The set up below shows how nitrogen gas is prepared in a laboratory.
(a) Describe how nitrogen gas us formed in the flask.
(b). Nitrogen is inert, state one use of the gas based on this property.
ANSWERS
(a) Oxygen is used up
(b) Lighting of bulbs
A mixture contains ammonium chloride, copper (II) oxide and sodium chloride.
Describe how each o the substances can be obtained from the mixture.
ANSWERS
Heat the mixture to sublime the ammonium chloride.
Add water to dissolve the sodium chloride ; copper (ii) oxide does not dissolve Filter and evaporate the filtrate to obtain sodium chloride.
Complete the nuclear equation below:
(c) Give one harmful effect of radioisotopes.
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