KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
The relative formula mass of a hydrocarbon is 58. Draw and name two possible structures of the hydrocarbon (C=12.0; H=1.0)
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a) Explain why permanent hardness in water cannot be removed by boiling.
b) Name two methods that can be used to remove permanent hardness from water.
ANSWERS
(a) The calcium and magnesium compounds in this water can not be decomposed by heating i.e. CaCl2, CaSO4, MgSO4 and MgCl2
(b)Ionic exchange Uses sodium carbonate (washing soda)
a) Distinguish between nuclear fission and nuclear fusion.
b) Describe how solid wastes containing radioactive substances should be disposed of.
ANSWERS
(a) Nuclear fusion is where two light nuclei combine to give a heavy release of energy while nuclear fusion is where a large nuclear splits into smaller nuclei with the release of enormous amount of energy.
(b) Wrap with aluminium or lead foil and bury them deep underground
a) name the process that takes place when:
(i) Crystals of zinc nitrate change into solution when exposed to air (ii) An alcohol reacts with an organic acid in the presence of a catalyst to form a sweet smelling compound. b) Propane can be changed into methane and ethane as shown in the equation below;
Name the process undergone by propane.
ANSWERS
(a) (i) Deliquescence
(ii) Esterification (b) Thermal cracking
a) State the Charles law
b) The volume of a sample of nitrogen gas at a temperature of 291 K and 1.0x105 Pascal‟s was 3.5 x 10-2m3. Calculate the temperature at which the volume of the gas would be 2.8 x 10-2m3 at 1.0 x 105 Pascal.
ANSWERS
ANSWERS
a)Dilute Nitric acid
b)Silver metal c)oxygen
Explain why there is general increase in the first ionization energies of the elements in period 3 of the periodic table from left to right.
ANSWER
In an experiment, a few drops of concentrated nitric acid were added to aqueous iron(II) sulphate in a test – tube. Excess sodium hydroxide solution was then added to the mixture.
a) State the observations that were made when: i) Concentrated nitric acid was added to aqueous iron (II) sulphate ii) Excess sodium hydroxide was added to the mixture. b) Write and ionic equation for the reaction which occurred in (a) (ii) above
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
ANSWERS
C- unburnt gas
D- Luminous yellow flame
Both chlorine and iodine are halogens.
a) What are halogens? b) In terms of structure and bonding, explain why the boiling point of chlorine is lower than that of iodine.
ANSWERS
(a) Group (VIII) elements
(b) Chlorine molecule is smaller and the strength of Vander Waals forces between molecules of chlorine is weak as compared to iodine.
15.0cm3 of ethanoic acid (CH3COOH) was dissolved in water to make 500cm3 of solution. Calculate the concentration of the solution in moles per litre. (C=12.0;H=1.0;O=16.0; density of ethanoic acid is 1.05 g/cm3)
90cm3 of 0.01M calcium hydroxide were added to a sample of water containing 0.001 moles of calcium hydrogen carbonate. a) Write an equation for the reaction which took place b) Calculate the number of moles of calcium ions in 90cm3 of 0.01M calcium hydroxide. c) What would be observed if soap solution was added drop wise to a sample of the water after the addition of calcium hydroxide? Give a reason. A gas occupies a volume of 400cm3 at 500k and 1 atmosphere pressure. What will be the temperature of the gas when the volume and pressure of the gas is 100cm3 and 0.5 atmospheres respectively. In an equation below, identify the reagent that acts as abase. Give a reason. H2O(aq) + H2O(l) → H3O(aq) + HO2-(aq) When 0.6g of element J were completely burnt in oxygen and all the heat evolved was used to heat 500cm3 of water, the temperature of the water rose from 230C to 320C. Calculate the relative atomic mass of element J given that the specific heat capacity of water = 4.2JK-1g-1, density of water = 1.0g/cm3 and molar heat is combustion of J is 380Kjmol-1
Potassium sulphite solution was prepared and divided into two portions. The first portion gave a white precipitate when reacted with barium nitrate. On addition of dilute hydrochloric acid the white precipitate disappeared.
a) Write the formula of the compound which formed as the white precipitate. b) Write the equation for the reaction between dilute hydrochloric acid and the compound whose formula is written in (a) above. c) What observation would be made if one drop of potassium dichromate solution was added to the second portion followed by dilute hydrochloric acid?
In an experiment, chlorine gas was passed into moist hydrogen sulphide contained in a boiling tube as shown in the diagram
a) What observation was made in the boiling tube?
b) Write an equation for the above reaction. c) What precaution should be taken in carrying out this experiment? Give a reason.
Explain why anhydrous magnesium chloride is fairly soluble in organic solvents while anhydrous magnesium chloride is insoluble.
Expected Response
Aluminum chloride is covalent while magnesium chloride is ionic
0.63g of lead powder were dissolved in excess nitric acid to form lead nitrate solution. All the lead nitrate solution was reacted with sodium sulphate solution.
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