KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Study the flow chart below and answer the questions t hat follow.
Identify Z and M.
Z……………………… M……………………
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One of the ores of copper has formula, CuFeS2.
(a) Describe how iron in the ore is removed during concentration of copper metal. (b) State two environmental problems associated with extraction of copper metal.
The table below shows the relative molecular masses and boiling points of pentane and ethanoic acid
Explain the large difference in boiling point between ethanoic acid and pentane.
ANSWERS
(a) Draw and name the isomers of butyne
(b) State one use of polystyrene.
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)
Explain how condition of electricity takes place in the following.
(a) Iron metal (b) Molten lead (II) iodide
ANSWERS
(a) delocalised electrons.
(b) Ions in the melt.
Starting with zinc sulphate solution, describe how a sample of zinc oxide can be obtained
Dry ammonia gas was passed over heated lead (II) oxide and the product passed over anhydrous Copper (II) sulphate as shown in the diagram below.
State:
(a)Two observations made in the combustion tube. (b) The property of ammonia gas shown in this experiment
ANSWERS
(a)The anhydrous copper (II) Sulphate turns from white to blue.
A grey solid is formed/droplets of a colourless liquid condense at cool part (b)Reducing property.
When dilute hydrochloric acid was reacted with solid B, a colourless gas which extinguished a burning splint was produced. When an aqueous solution of solid B was tested with a blue litmus paper, the paper turned red / pink.
(a) Identify the anion present in solid B. (b) Write an ionic equation for the reaction between solid B and dilute hydrochloric acid.
The flow chart in Figure 1 represents some stages in the extraction of copper metal. Study it and answer the questions that follow.
Identify:
Describe how an increase in concentration increases the rate of a reaction. (2 marks)
Expected Response
As the concentration increases the number of reactivity of particles per unit volume increases thus affecting collisions. This leads to increase in the rate of reaction
An atom of element A has mass number 39 and 19 protons.
Explain how the hotness of a Bunsen burner flame can be increased
ANSWER
a) Study the information in the table below and answer the questions that follow.
(The letters do not represent the actual symbols of the elements).
c) Neutralization is one of the methods of preparing salts. i) What is meant by neutralization? ii) Describe how you would prepare crystals of sodium nitrate starting with 200cm3 of 2M sodium hydroxide. iii) Write an equation for the reaction that takes place when a solid sample of sodium nitrate is heated.
(Fe - = 56.0,Cl = 35.5 and Molar gas volume at 298K is 24,000cm3
C) When hydrogen sulphide gas was passed through a solution of iron (III) chloride, the following observation were made:
a) Fraction distillation of liquid air usually produces nitrogen and oxygen as the major products.
(Boiling points nitrogen = - 1960C, oxygen = -1830C)
b) Study the flow chart below and answer the questions that follow.
The Ph of a sample of soil was found to be 5.0.An agricultural office recommended the addition of calcium oxide in the soil. State two functions of the calcium oxide in the soil.
Expected Response
Hydrogen peroxide decomposes according to the equation below:
8.5 gm of hydrogen peroxide contained in 100cm3 of solution with water were completely decomposed. Determine the rise in temperature due to the reaction. Specific density of water = 1g/cm3 O =16, H = 1,).
Expected Response
In an experiment to study the rate for reaction between duralumin (an alloy of aluminium, magnesium and copper) and hydrochloric acid, 0.5g of the alloy were reacted with excess 4M hydrochloric acid. The data in the table below was recoded.
Use it to answer the questions that follow. a) i) On the grid provided, plot a graph of total volume of gas produced (vertical axis) again time. ii) From the graph, determine the volume of gas produced at the end of 2 ½ minutes. b) Determine the rate of reaction between the 3rd and 4th minute. c) Give a reason why some solid remained at the end of the experiment d) Given that 2.5cm3 of the total volume of the gas was from the reaction between magnesium and aqueous hydrochloric acid, calculate the percentage mass of aluminium present in 0.5g of the alloy. (Al = 27.0 and Molar gas volume = 24,000cm3 at 298k) e) State two properties of duralumin that make it more suitable than aluminium in aeroplane construction. a) In which homologous series do the following compounds belong i) CH3CC ii) CH3CH2COO
b) Raw rubber is heated with sulphur in the manufacture of natural rubber.
i) What is the name given to the process ii) Why is the process necessary?
c) Study the scheme given below and answer the questions that follow
i) Write an equation for the reaction between propane – 1 – 0 / and potassium metal.
ii) Name processes I and II I II iii) Identify the products A and B iv) Name one catalyst used in process II v) Draw the structural formular of the repeating unit in the polymer C. d) State two industrial uses of methane.
a) Study the standard electrode potentials do the half – cells given below and
answer the questions that follow. (The letters do nor represent the actual symbols of the elements.)
i) Identify the strongest oxidizing agent. Give a reason for your answer.
ii) Which two half – cells would produce the highest potential difference when combined? iii) Explain whether the reaction represented below can take place. b) 100cm3 of 2M sulphuric acid was electrolysed using the set – up represented by the diagram below.
i) Write an equation for the reaction that produces gas L.
ii) Describe how gas K can be identified iii) Explain the difference in : I The volume of the gases produced at the electrodes. II Brightness of the bulb if 100cm3 of 2M ethanoic acid was used in place of sulphuric acid.
(a) Give the systematic names for the following compounds
(b) Study the flow chart below and use it to answer the questions that follow
(i) Identify the organic compound K
(ii) Write the formula of M (iii) Give one reagent that can be used in (a) Step I (b) Step II (iv) Write the equation of the reaction in step III (c) The structure below represents a type of a cleaning agent
Describe how the cleansing agent removes grease from a piece of cloth
(a) distinguish between a neutron and proton
(b) What is meant by a radioactive substance? (c) State two dangers associated with radioactive substance in the environment
(i) What is the atomic
a. Mass of Y b. Number of Y (ii) What name is given to the type of reaction undergone by the isotopes of hydrogen? (e)(i) What is meant by half-life of a radioactive substance (ii) 288 g of a radioactive substance decayed to 9 g in 40 days. Determine the half-life of the radioactive substance
(a) describes one method that can be used to distinguish between sodium sulphate and sodium hydrogen sulphate.
b) Describe how a pure sample of lead (II) sulphate can be prepared in the laboratory starting with lead metal c) Study the flow chart below and answer the questions that follow:
i) Write an equation for the reaction in:
I step II; II step IV ii) State the observation made in step III. Explain. iii) Name another substance that can be used in step V.
ANSWERS
(a)Test the acidity using a litmus pager. There will be no change on litmus when dipped into a solution of sodium sulphate . The litmus paper turns to red when dipped into a solution of sodium hydrogen sulphate .
OR Add a solid carbonate to each solution. No effervescence observed when the carbonate is added to a solution of sodium sulphate. Effervescence is observed when the carbonate is added to a solution of sodium hydrogen sulphate. (b)Add dilute nitric acid to lead to form a soluble salt, Pb(NO3)2, add a soluble salt, Na2SO4. Then dry the salt between filter papers . (c)(i) NH4 NO3 → N2O + 2H2O II 2Fe(OH)3(S) → Fe2O3(s) + 3H2O(l) (ii) The colour changes from pale green to brown . The iron (II) is oxidised to iron (III) chloride by hydrogen peroxide (iii) Carbon monoxide |
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