KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
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
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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?
The table below shows the volumes of nitrogen dioxide gas produced when different volume of 1M nitric acid were each reacted with 2.07 g of lead at room temperature.
a) Give a reason why nitric acid is not used to prepare hydrogen gas. b) Explain how the rate of the reaction between lead and nitric acid would be affected if the temperature of the reaction mixture was raised. c) On the grid provided below, plot a graph of the volume of the gas produced (Vertical axis) against volume of acid.
d) Using the graph, determine the volume of
:i) Nitrogen dioxide produced when 30cm3 of 1 M nitric acid were reacted with 2.07 g of lead ii) 1M nitric acid which would react completely with 2.07g of lead. e) Using the answer in d(i) above, determine: i) The volume of 1M nitric acid that would react completely with one mole of lead (Pb=207) ii) The volume of nitrogen dioxide gas produced when one mole of lead reacts with excess 1 M nitric room temperature. f) Calculate the number of moles of: i) 1M nitric acid that reacted with one mole of lead ii) nitrogen dioxide produced when one mole of lead were reacted with excess nitric acid. (Molar gas volume of 2400cm3) g) Using the answers obtained in f (i) and (ii) above, write the equation for the reaction between lead and nitric acid given that one mole of lead nitrate and two moles of water were also produced.
The extraction of iron from its ores takes place in the blast furnace. Study it and answer the questions that follow.
a) Name
(i) One of the substances in the slag (ii) Another iron ore material used in the blast furnance. (iii) One gas which is recycled. b) Describe the process which leacd to the formation of iron in the blast furnace c) State the purpose of limestone in the blast furnace. d) Give a reason why the melting point of the iron obtained from the blast furnace is 12000 C while tat of pure iron is 15350C (e) State two uses of steel
a) What name is given to a compound that contains carbon and hydrogen only?
b) Hexane is a compound containing carbon and hydrogen. (i) What method is used to obtain hexane from crude oil? (ii) State one use of hexane c) Study the flow chart below and answer the questions that follow.
(i) Identify reagent L.
(ii) Name the catalyst used in step 5. (iii) Draw the structural formula of gas J. (iv) What name is given to the process that takes place in step 5? d) (i) write the equation for the reaction between aqueous sodium hydroxide and aqueous ethanoic acid. (ii) Explain why the reaction between 1g of sodium carbonate and 2M hydrochloric acid is faster than the reaction between 1g of sodium carbonate and 2M ethanoic acid.
a) In an experiment to determine the molar heat of reaction when magnesium displaces copper ,0.15g of magnesium powder were added to 25.0cm3 of 2.0M copper (II) chloride solution. The temperature of copper (II) chloride solution was 25°C.While that of the mixture was 43°C.
i) Other than increase in temperature, state and explain the observations which were made during the reaction. ii) Calculate the heat change during the reaction (specific heat capacity of the solution = 4.2jg-1k-1and the density of the solution = 1g/cm3 iii) Determine the molar heat of displacement of copper by magnesium.(Mg=24.0). iv) Write the ionic equation for the reaction. v) Sketch an energy level diagram for the reaction. b) Use the reduction potentials given below to explain why a solution containing copper ions should not be stored in a container made of zinc.
a) What is an electrolyte?
b) State how the following substances conduct electricity. i) Molten calcium chloride ii) Graphite. c) The diagram below shows a set up that was used to electrolyse aqueous magnesium sulphate.
i) On the diagram above, using an arrow, show the direction of flow of electrons.
ii) Identify the syringe in which hydrogen gas would be collected. Explain d) Explain why the concentration of magnesium sulphate was found to have increased at the end of the experiment. e) During the electrolysis, a current of 0.72A was passed through the electrolyte for 15 munities. Calculate the volume of gas produced at the anode.(1 Faraday = 96 500 coulombs; molar gas volume is 24000cm3 at room temperature).
Explain why the boiling point of ethanol is higher than that of hexane.
(Relative molecular mass of ethanol is46 while that of hexane is 86)
ANSWERS
(a) Explain why the metals magnesium and aluminium are good conductors of electricity.
b) Other than cost, give two reasons why aluminium is used for making electric cables while magnesium is not
ANSWERS
a)They have delocalized valency electrons
b)Aluminium has three delocalized electrons. It is resistant to corrosion
a) starting from solid magnesium hydroxide.
b) Give one use of magnesium hydroxide.
Study the standard reduction potential given and answer the questions that follow.
(The letters are not the actual symbols of the elements).
a) The standard reduction potential for Fe 2+(aq) is -0.44 volts. Select the element which would best protect iron from rusting.
b) Calculate the E ø value for the cell represented as M(s) / M2+ (aq) // P+(aq) /P(s).
Below is a list of oxides.MgO, N2O, K2O, CaO, and Al2O3.
Select: a) A neutral oxide b) A highly water soluble basic oxide c) An oxide which can react with both sodium hydroxide solution and dilute hydrochloric acid.
a) water from a town in Kenya is suspected to contain chloride ions but not sulphate ions.
Describe how the presence of the chloride ions in the water can be shown. b) State one advantage of drinking hard water rather than soft water.
ANSWERS
a)
Acidify water with nitric acid. Add aqueous lead nitrate. Formation of white PPt shows presence of CT b)provides essential minerals e.g Ca2+
ANSWERS
The information below relates to element L, Q, R and T. The letters do not represent the actual symbols of the elements. Arrange the elements in
a) Give the formula of an oxide which reacts with both dilute hydrochloric acid and hot concentrated sodium hydroxide. b) Give the formulae of the products formed when the oxide in (a) above reacts with excess hot concentrated sodium hydroxide.
M grammes of a radioactive isotope decayed to 5 grammes in 100 days.
The Half – lift off the isotope is 25 days. a) What is meant by half – life? b) Calculate the initial mass of M of the radioactive isotope. |
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