KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
ANSWER
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In an experiment, a test-tube full of chlorine water was inverted in chlorine water as shown in the diagram below and the set up left in sunlight for one day.
After one day, a gas was found to have collected in the test-tube
a) Identify the gas. b) What will happen to the PH of the solution in the beaker after one day? Give an explanation.
A sample of water drawn from a river passing through an agricultural district was divided into two portions. The first portion gave a white precipitate when acidified barium chloride was added. The second portion when warmed with aqueous sodium hydroxide gave a colourless gas, which turned a moist red litmus paper blue.
On complete combustion of a sample of hydrocarbon, 3.52 gm of carbon dioxide and 1.44 gm of water were formed. Determine the molecular formula of the hydrocarbon.
(Relative molecular masses of hydrocarbon = 56, carbon dioxide 44, water = 18 and relative atomic masses H = 1.0 and c = 12.0)
Give one advantage and one disadvantage of using petrol containing tetraethyl lead in motor vehicles.
Expected Response
Advantage
Expected response
Add water to the solid mixture A dissolves while B does Not
The table below gives atomic numbers of elements represented b the letters A, B, C and D.
Use the information to answer the questions that follow.
a) Name the type of bonding that exists in the compound formed when A and D react b) Select the letter which represents the best oxidizing agent. Give a reason for your answer.
ANSWERS
(a)Ionic/ electrovalent
(b)Has 7 electrons in its outermost energy level and hence easily gains an electron to complete the octet or it is most electronegative.
When magnesium was burnt in air, a solid mixture was formed. On addition of water to the mixture a gas which turned moist red litmus paper blue was evolved. Explain these observations.
Zinc reacts with both concentrated and dilute sulphuric (VI) acid. Write equations for two reactions.
a) State the observation made at the end of the experiment when a mixture of iron powder and sulphur is heated in a test tube.
b) Write an equation for the reaction the product in (a) above and dilute hydrochloric acid. c) When a mixture of iron powder and sulphur is heated, it glows more brightly than that of iron fillings and sulphur. Explain this observation
ANSWERS
An isotope of Uranium 234U, decays by emission of an alpha particle to thorium 92
ANSWERS
Phosphoric acid is manufactured from calcium phosphate according to the following equation.
Ca3(PO4)2(s) + 3H2SO4(l) → 2H3PO4(aq) + 3 CaSO4(s) Calculate the mass in (Kg) of phosphoric acid that would be obtained if 155 Kg of calcium phosphate reacted completely with the acid (Ca=40, P=31, S=32, O=16, H=1)
The structure of a detergent is
a) Write the molecular formula of the detergent.
b) What type of detergent is represented by the formula? c) When this type of detergent is used to wash linen in hard water, spots (marks) are left on the linen. Write the formula of the substance responsible for the spots
When a hydrated sample of calcium sulphate CaSO4 .XH2O was heated until all the water was lost, the following data recorded;
Mass of crucible = 30.296 g Mass of crucible +hydrated salt = 33.111 g Mass of crucible + anhydrous salt = 32.781 g Determine the empirical formula of the hydrated salt (Relative formula mass of CaSO4 =136, H2O =18).
(a) The diagram below represents a set up that was used to obtain dry nitrogen from air. Study it and answer the questions that follow
Related Chemistry Questions and Answers on ​nitrogen and its compounds form 3 levelThe reaction between and methanoic acid at 300C proceeds according to the information given below (a) On the grid below, plot a graph of concentration of Bromine (Vertical axis against time) (b) From the graph determine: (i) The concentration of bromine at the end of 3 minutes (ii) The rate of reaction at time ‘t’ where t = 1 ½ minutes (c) Explain how the concentration of bromine affects the rate of reaction (d) On the same axis sketch the curve that would be obtained if the reaction was carried out at 200C and label the curve as curve II. Give a reason for your answer.
A small crystal of potassium manganate (VII) was placed in a beaker water. The beaker was left standing for two days without shaking. State and explain the observations that were made.
ANSWERS
The diagram below shows the set up used in an experiment to prepare chlorine gas and react it with aluminium foil. Study it and answer the question that follow
(a) In the experiment, concentrated hydrochloric acid and potassium manganate (VII) were used to prepare chlorine gas. State two precautions that should be taken in carrying out this experiment.
(b) Write the formula of another compound that could be used instead of potassium manganate (VII) (c) Explain why it is necessary to allow the acid to drip slowly onto potassium manganate (VII) before the aluminium foil is heated. (d) State the property of the product formed in the combustion tube that makes it possible for it to be collected in the receiver (e) When 1.08g of aluminum foil were heated in a stream of chlorine gas, the mass of the product formed was 3.47 g Calculate the: (i) Maximum mass of the product formed if chlorine was in excess; (Al= 27; Cl = 35.5) (ii) Percentage yield of the product formed (f) Phosphorous trichloride is a liquid at room temperature. What modification should be made to set up if it is to be used to prepare phosphorous trichloride?
(a) The elements nitrogen, phosphorous and potassium are essential for plant growth.
(i) Potassium in fertilizers may be in the form of potassium nitrate Describe how a sample of a fertilizer may be tested to find out if it contained nitrate ions. (ii) Calculate the mass of nitrogen present if a 25kg bag contained pure ammonium phosphate, (NH4)2 HPO4. (N = 14.0, H=1.0, P = 31.0, O = 16.0 (b) The table below shows the solubility of ammonium phosphate in water at different temperatures.
(i) On the grid provided, draw the solubility curve of ammonium phosphate (Temperature on x – axis)
(ii) Using the graph, determine the solubility of ammonium phosphate at 25°C (iii) 100g of a saturated solution of ammonium phosphate was prepared at 25°C I what is meant by a saturated solution? II Calculate the mass of ammonium phosphate which was used to prepare the saturated solution (c) The graph below shows how the PH value of soil in a farm changed over a period of time
(i) Describe how the pH of the soil can be determined
(ii) State one factor that may have been responsible for the change in the soil pH in the time interval AB |
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