KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
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.
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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.
The curve below represents the changes in the concentration of substance E and F with time
In the reaction; E (g) ⇄ F(g)
(i) Which curve represents the changes in concentration of substance F? Give a reason
(ii) Give a reason for shapes of curves after time ‘t’ minutes
Use the information below to answer the question that follows
(a) A few drops of freshly prepared iron (II) sulphate solution were added to potassium nitrate solution in a test – tube. Concentrated sulphuric acid was then carefully added to the mixture. State the observation that were made
(b) Write an equation for the reaction that occurs when solid potassium nitrate is strongly heated
Use the cell representation below to answer the questions that follow
In an attempt to prepare sulphur dioxide gas, dilute sulphuric acid was reacted with barium sulphuric. The yield of sulphur dioxide was found to be negligible explain
The pressure of nitrogen gas contained in a 1dm3 cylinder at -196°C was 107 Pascals.
Calculate the: a) Volume of the gas at 25°C and 105 Pascals. b) Mass of nitrogen gas(Molar volume of gas is 24dm3, N = 14.0)
Complete the table below by writing the product formed at the electrodes during the electrolysis of the electrolytes given in the table.
Aluminium oxide reacts with both acids and bases.
a) Write an equation for the reaction between aluminium oxide and hydrochloric acid. b) Using the equation in (a) above, calculate the number of moles of hydrochloric acid that would react completely with 153.0g of aluminium oxide. (AL = 27.0, 0= 16.0)
Hydrate cobalt(II) chloride exists as pink crystals and anhydrous cobalt(II) chloride is a blue powder. Describe a laboratory experiment that can be used to show that the action of heat on hydrated cobalt(II) chloride is a reversible reaction.
Draw the structures and give the name of the three alkaline having molecular formula C5H10
What is the name given to each of the following:
a) What is meant by the terms: i. element ii. atomic number
b) The formula for a chloride of titanium is TiCl3. What is the formua of its sulphate?
ANSWERS
(i) Element — substance that consists of one type of atoms.
(ii) Atomic number — number of protons in an atom. Ti3(S04)2 |
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