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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
The empirical formula of a hydrocarbon is (CH2). It has a density of 0.001167g/cm3 at room temperature and pressure. (Molar gas volume at r.t.p is 24dm3)a) Determine the molecular formula of the hydrocarbon (3mks)
b) Draw the structural formula of the hydrocarbon (1mk)
c) Ethene gas burns in Oxygen to form Carbon (IV) oxide and water.i) Write an equation for the reaction between ethane gas oxygen gas (1mk)
ii) 15cm3 of ethene gas were mixed with 50cm3 of oxygen gas and the mixture was ignited into complete combustion. Calculate the volume of excess unreacted gas (3mks)
d) What happens when ethene gas is bubbled through bromine water? (2mks)
e) Give any two uses of ethene gas (2mks)
Uses of Ethene gas
Name one gas used together with oxygen in welding other than acetylene gas (1mk)
Hydrogen
State two other uses of the gas named above (2mks)
(a) State Graham’s law of diffusion
(b) Explain why a balloon filled with helium gas deflates faster than a balloon of the same size filled with argon gas.
ANSWERS
(a) Graham’s Law of diffusion
The rate of diffusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure. (b)Helium is less dense than argon hence it diffuses out of the balloon faster than argon.
(a) State Charles' Law.
(b) Explain why the pressure of a fixed mass of a gas increases, when the volume of the gas is reduced at constant temperature.
ANSWERS
(a)The volume of a fixed mass of a gas is directly proportional to the absolute temperature at constant pressure.
(b)As the volume decreases, there is increased bombardment / collisions of the molecules against the walls of the container, hence increased pressure.
60 cm3 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)
ANSWERS
140cm3 of nitrogen gas diffuses through a membrane in 70 seconds. Flow long will it take 200cm3 of carbon(IV) oxide gas to diffuse through the same membrane under the same conditions of temperature and pressure. (3 marks)
Expected Response
a) State the Boyles Law
b) A gas occupies 500cm3 at 27°C and 100,000 Pa, What will be its volume at O°C and 101325 Pa?
ANSWERS
(a) Boyle’s law: The volume of a fixed mass of a gas is inversely proportional to its pressure or the product of pressure and volume is constant at a fixed temperature.
100cm3 of a sample of ethane gas diffuses through a porous pot in 100 seconds. What is the molecular mass of gas Q if 1000 cm3 of the gas diffuses through the same porous not in 121 seconds under the same conditions? (C=12.0, H=1.0)
ANSWERS
(a) State the Charles’ law
(b) A certain mass of gas occupies 146 dm3 at 291 K and 98.31 kPa. What will be its temperature if its volume is reduced to 133 dm3 at 101.325 kPa?
ANSWERS
The set up shown below was used to investigate a property of hydrogen gas.
State and explain the observation that would be made in the glass tube if beaker A was filled with hydrogen gas.
ANSWERS
In an experiment, ammonia chloride was heated in a test tube. A moist red litmus paper placed at the mouth of the test tube first changed blue then red. Explain these observations
Expected Response
NH4Cl decomposes to form NH3(g) and HCl(g).Ammonia diffuses faster than HCl because its light. Ammonia is basic and thus red litmus paper turns blue while HCl is acid thus blue litmus turns red.
A given volume of ozone, (O3) diffused from a certain apparatus in 96 seconds. Calculate the time taken by an equal volume of carbon dioxide (CO2) to diffuse under the same conditions (O = 16.0, C = 12.0)
Expected Response
(a) State the Gay Lussac's Law.
(b) 10cm3 of a gaseous hydrocarbon, C2HX required 30cm3 of oxygen for complete combustion. If steam and 20cm3 of carbon (IV) oxide were produced, what is the value of X?
ANSWERS
A certain mass of gas occupies 0.15dm3 at 293K and 98,648.5Pa. Calculate its Volume at 101,325Pa and 273K.
ANSWERS
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January 2025
AuthorMaurice Atika is a teacher and a netprenuer. |
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