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​These are chemistry questions and answers categorized according to topics, papers i.e. Paper 1 and 2, Levels i.e. form 1 to form 4, kcse year the examination was done and section A or B
Select topic/category to open topical questions from that particular option provided. ​Chemistry Topics
Define oxidation and reduction in terms of electrons
Oxidation is the loss of electrons while reduction is gain electrons
Calculate the oxidation number of Chromium in Cr2O2- (1mk)
x * 2+(-2)=-2
The flow chart in Figure 3 shows the process of obtaining a sample of nitrogen gas. Study it and answer the questions that follow.
(a) Identify X
(b) Write an equation for the reaction with heated copper turnings. (c) Name an impurity in the sample of nitrogen gas.
ANSWERS
Potassium nitrate liberates oxygen gas when heated. Draw a diagram of a set-up that shows heating of potassium nitrate and collection of oxygen gas.
ANSWERS
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.
ANSWERS
When solid A was heated strongly, it gave off water and a solid residue. When water was added to the solid residue, the original solid A, was formed
(a) What name is given to the process described? (b) Give one example of solid A
ANSWERS
(a)Type of reaction: Reversible reaction/temporary reaction.
(b)Copper (II) Sulphate salt (Crystals) Copper (II) Chloride hydrated. Any other hydrated salts e.g. Cobalt (II) Chloride
A measuring cylinder fitted with moist steel wool was inverted in a trough of water as shown in the diagram below
(a)State and explain the observations made on the;
i) Moist steel wool after four days. ii) Water level in the measuring cylinder after four days. (b) What would be the effect of using steel wool moistened with salty water?
ANSWERS
(a) (i) It turned brown /blue/violet/green.
(ii) The water level rose up the gas jar/occupy space left by reacted 02 (b) The brown colour would be more since the salt accelerates rusting/rust faster.
The diagram below shows an iron bar, which supports a bridge. The Iron bar is connected to a piece of magnesium metal
Explain why it is necessary to connect the piece of magnesium metal to the iron bar.
Expected Response
Magnesium is above iron in the activity series. It supplies electrons to the iron bar Hence prevent it from rusting
The set up below can be used to prepare oxygen gas. Study it and answer the questions that follow.
(a) Identify X
(b) What property of oxygen makes it possible for it to be collected as shown in the above set up? (c) State two uses of oxygen
ANSWERS
The following set up of three test-tubes was used to investigate rusting of iron.
Study it and answer the questions that follow. 
(a) Give a reason why rusting did not occur in test-tube C.
(b) Aluminium is used to protect iron sheets from rusting. Explain two ways in which aluminium protects iron from rusting.
ANSWERS
(a) No air due to boiling.
(b) Aluminium being very reactive forms a layer of Al2O3 on the metal making it impervious to moisture. Aluminium being more reactive than iron protects the iron through sacrificial protection cathodic protection.
Name another gas, which is used together with oxygen in welding
Expected Response
Acet5ylene (ethyne) or Hydrogen
In an experiment, dry hydrogen gas was passed over heated Lead (II) Oxide as shown in the diagram below.
State and explain the observations made in the combustion tube.
ANSWERS
Use the information in the table below to answer the questions that follows
Explain the trend in the molar heats of vaporization
Expected Response
Change was greatest with magnesium. Both react with oxygen to form oxides but magnesium reacts with nitrogen to form a nitrite
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.
ANSWERS
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.
ANSWERS
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December 2024
AuthorMaurice Atika is a teacher and a netprenuer. |
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