KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
(a) What name is given to the process by which alcohol is formed from a carbohydrate?
(b) Explain why the solubility of ethane in water is lower than that of ethanol.
ANSWERS
(a) Fermentation.
(b) Ethane remains in molecular form while ethanol forms hydrogen bonds with water.
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Under certain conditions, carbon dioxide reacts with water to form methanol (CH3OH) and oxygen as shown below
What would be the effect on the yield of methanol if the temperature of the reaction mixture is increased? Explain
In an experiment a certain volume of air was passed from syringe to syringe over heated zinc powder as shown in the diagram below
The experiment was repeated using excess magnesium powder. In which of two experiments was the change in volume of the air greatest. (Give reasons)
The set up below was used to investigate some properties of two gases M and N
The diagram below shows a set up for the laboratory preparation and collection of dry chlorine gas
Expected Response
Molar heats of vaporization increase down the group with increase in van der waals forces of attraction as the number of electrons increase/increases in size/ volume/mass/energy levels/ density/ No. of protons (atomic number)
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
The set up below was used to investigate some properties of two gases M and N
When beaker A was filed with gas M, the level of water in the glass tube rose to
point II. When the experiment was repeated using gas N, the level of water dropped to point III. Explain these observations.
The atomic numbers of phosphorus, sulphur and potassium are 15, 16 and 19 respectively. The formulae of their ions are P3-,S2- and K+. These ions have the same number of electrons.
a) Write the electron arrangement for the ions. b) Arrange the ions in the order of increasing ionic radius starting with the smallest. Give a reason for the order.
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.
A sample of river water was divided into three portions. The table below shows the test carried out on the portions and the observations made.
Complete the table by filling in the inferences.
Describe how a solid sample of the double salt, ammonium iron(II) sulphate, can be prepared using the following reagents; Aqueous ammonia, sulphuric(VI) acid and iron metal.
ANSWERS
The curves below shows how the electronic conductivity of hydrochloric and ethanoic acids vary with concentration.
Explain why the electrical conductivity of 0.01M hydrochloric acids is higher than that of 0.01M ethanoic acid.
ANSWERS
Nitrogen and hydrogen react to form ammonia gas as shown in the following equation:
a) The figure below shows how the percentage of ammonia gas in the equilibrium mixture change with temperature.
Explain why the percentage of ammonia gas change as shown in the figure.
b) On the axes below, sketch a graph showing how the percentage of ammonia gas in equilibrium mixture changes with pressure.
The use of CFCs has been linked to depletion of the ozone layer.
a) What does CFC stand for? b) Explain the problem associated with the depletion of the ozone layer c) State another environment problem caused by CFCs
ANSWERS
(a)Chlorofluorocarbon
(b)When ozone is depleted, high energy UV radiations reach the earth, which may cause skin cancer to human beings. (c)Global warmings, /green house effect.
In an experiment to prepare nitrogen (I) oxide, ammonium nitrate was gently heated in a flask.
a) Write the equation for the reaction that took place in the flask. b) State and explain how the gas was collected. c) A sample of the gas was tested with damp blue and red litmus papers. What observations were made?
The half equations involved in a cell are:
2H2O(l) + 2e = H2(g) + 2OH-(aq): Eθ = - 0.83V O2(g) + 2H2O(l) + 4e = 4OH-(aq): Eθ = + 0.40V a) Write the overall equation for the electrochemical cell. b) Calculate he e.m.f. generated by a battery consisting of ten cells. c) State one environment advantage of using these cells in spacecrafts.
The diagram below represents set up for large scale manufacture of hydrochloric acid.
Study it and answer the questions that follow.
a) Name substance X
b) What is the purpose of the glass beads? c) Give two uses of hydrochloric acid.
Analysis of a compound showed that it had the following composition: 69.42% carbon, 4.13% hydrogen and the rest oxygen.
a) Determine the empirical formula of the compound. (C = 12.0, H = 1.0, O = 16.0) b) If the mass of one mole of the compound is 242, determine its molecular formula
A sample of fertilizer is suspected to be calcium ammonium nitrate. Describe chemical tests for each of the following ions in the sample:
a) Calcium ions; b) Ammonium ions.
ANSWERS
(a)Add a few drops of NaOH to an aqueous solution of the fertilizer. Forms white precipitate insoluble in excess. .
Add a few drops of aqueous sulphuric (VI) acid to another portion of aqueous solution of fertilizer. Forms a white precipitate insoluble in excess. (b)Heat the sample fertilizer in a test tube, and test gas evolved with damp red litmus paper, turn blue. Or add NaOH to the sample fertilizer and heat the mixture; test gas evolved using damp red litmus paper, turn blue.
Carbon (II) oxide is described as a “silent killer”
a) State one physical property of carbon (II) oxide that makes it a “silent killer” b) State and explain one chemical property that makes carbon (II) oxide poisonous to human beings
ANSWERS
(a)gas has no colour and smell.
(b)Carbon (II) oxide has high affinity for iron in the haemoglobin in the blood, or displaces oxygen from haemoglobin, the body tissues are deprived of oxygen.
Using electrons in thee outermost energy level, draw the dot (.) and cross (x) diagrams for the molecules H2O and C2H4. (H = 1, C = 6, O = 8)
i) H2O ii) C2H4 b) The formula of a complex ion is Zn(NH3)42+. Name the type of bond that is likely to exist between zinc and ammonia in the complex ion.
Some animal and vegetable oils are used to make margarine and soap. Give the reagents and conditions necessary for converting the oils into:
a) Margarine b) Soap
A beaker contained 75.0cm3 of aqueous copper (II) sulphate at 23.7°C. when scrap iron metal was added to the solution, the temperature rose to 29.3°C.
a) Write an ionic equation for the reaction that took place. b) Given that the mass of copper deposited was 5.83g, calculate the molar enthalpy change in kJmol-1. (specific heat capacity of solution = 4.2Jg-1 K-1, density of solution 1.0gcm-3, Cu = 63.5)
Hydrogen sulphide is a highly toxic and flammable gas. It is normally prepared in a fume chamber
.a) Name two reagents that can be used to prepare hydrogen sulphide in the laboratory. b) One of the uses of hydrogen sulphide is to produce sulphur as shown in the following equation; 2H2S(g) + SO2(g) → 3S(s) + 2H2O(l) Identify the reducing agent in this reaction and give a reason for your answer. c) Other than production of sulphuric(IV) acid, state one commercial use of sulphur.
ANSWERS
(a) Iron (II) Sulphide
Hydrochloric acid (b)Reducing agent, hydrogen sulphide The sulphur changes from -2 to zero (c) Vulcanization of rubber Manufacture of sulphur drugs
The figure below shows an energy cycle.
a) Give the name of the enthalpy change ΔH1.
b) Determine the value of ΔH3.
a) Write a nuclear equation for the decay process of carbon -14.
b) From the graph, determine the; i) Half-life of carbon -14; ii) Percentage of carbon -14 in a sample whose age is 1950 years. |
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