KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
The table below shows the relative atomic masses and the percentage abundance of the isotopes L1 of element L.
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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+
Name the process which takes place when:
a) Solid carbon (IV) oxide (dry ice) changes directly into gas b) A red litmus paper turns white when dropped into chlorine water. c) Propane gas molecules are converted into a giant molecule
ANSWERS
a)sublimation
b)Bleaching. c)Polymerization
ANSWERS
When 94.5g of hydrated barium hydroxide, ba(OH)2. nH2O were heated to constant mass, 51.3g of anhydrous barium hydroxide were obtained. Determine the empirical formula of the hydrated barium hydroxide.
A group of compounds called chlorofluorocarbons have a wide range of uses but they also have harmful effects on the environment.
State one: a) Use of chlorofluorocarbons b) Harmful effect of chlorofluorocarbons on the environments.
ANSWERS
a)Refrigeration
b) - They deplete the ozone layer. - They cause green house effect.
In an experiment to study the properties of concentrated sulphuric acid, a mixture of the acid and wood charcoal was heated in a boiling tube.
(a) write the equation of the reaction that took place in the boiling tube. (b) Using oxidation numbers, show that reduction and oxidation reactions took place in the boiling tube
The atomic numbers of elements C and D are 19 and 9 respectively. State and explain the electrical conductivity of the compound CD in:
(a) Solid state (b) aqueous state.
ANSWERS
60cm3 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)
The diagram below represent a set-up that was used to show that part of air is used during burning.
a) Given that phosphorus used was was in excess, draw a diagram of the set-up at the end of the experiment (when there was no further observable change).
b) Suggest one modification that should be made on the apparatus if the percentage of the air used is to be determined.
(a) In an experiment, dry hydrogen chloride gas was passed through heated zinc turnings as shown in the diagram below. The gas produced was then passed through heated lead (II) oxide.
Calculate the mass of nitrogen dioxide gas that would occupy the same volume as 10g of hydrogen gas at same temperature and pressure.(H = 1.0, N = 14.0, o = 16.0)
Using dots (.)and crosses (x) to represent outermost electrons, draw diagrams to show the bonding in CO2 and H3O+ (Atomic numbers; H = 1.0,C= 14.0, O = 8 ).
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.
Name and draw the structure of the compound formed when methane reacts with excess chlorine in the presence of U.V light.
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.
When dilute nitric acid was added to a sample of solid C, a colourless gas that formed a white a white precipitate with lime water was produced. When another sample of solid C was heated strongly in a dry test – tube, there was no observable change.
When extinguishing a fire caused by burning kerosene, carbon dioxide is used in preference to water .Explain
Expected Response
- Kerosene floats on water therefore it continues to burn
- Carbon dioxide blanket covers the flame OR cuts off the supply of oxygen
Expected Response
- Iron wool turns or rusts due to formation of hydrated iron (III) oxide
- Level of water inside the tube rises to occupy the space left by oxygen - Level of water in the beaker will fall |
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