KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Dry ammonia and dry oxygen were reacted as shown in the diagram below
a)What is the purpose of the glass wool?
b) What products would be formed if red hot platinum was introduced into a mixture of ammonia and oxygen?
ANSWERS
(a)The purpose of the glass wool. It spreads the oxygen evenly/increase surface area or enriches the air with oxygen.
(b)Forms NO, Nitrogen (II) Oxide and steam
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The curve shown below shows the variation of time against temperature for the reaction between sodium thiosulphate and hydrochloric acid.
a) Write the equation for the reaction between sodium thiosulphate and dilute hydrochloric acid
b) Explain the shape of the curve
ANSWERS
Dilute sulphuric (VI) acid was electrolysed using platinum electrodes.
Name the product formed at the anode and give a reason for your answer.
The atomic number of an element, T is 15.
(a) Write the electronic configuration of the ion T (b) Write the formula of an oxide of T.
The set up below was used to investigate the reaction between dry hydrogen gas and copper (II) oxide
a) Name substance A
b) state the observation made in the combustion tube c) Explain the observation stated in (b) above.
ANSWERS
(a) Substance A - Calcium Oxide- fused calcium chloride
- Accept any other answer (b) Black Copper (II) Oxide (Solid) changes to brown Colourless liquid formed on the cooler part of the combustion tube. (c) Copper (II) Oxide is reduced to Copper metal.
When solid A was heated strongly, it gave off water and a solid residue. When water was added to the solid residue, the original solid A, was formed
(a) What name is given to the process described? (b) Give one example of solid A
ANSWERS
(a)Type of reaction: Reversible reaction/temporary reaction.
(b)Copper (II) Sulphate salt (Crystals) Copper (II) Chloride hydrated. Any other hydrated salts e.g. Cobalt (II) Chloride
Hydrogen chloride gas can be prepared by reacting sodium chloride with an acid.
(a) Write an equation for the reaction between sodium chloride and the acid. (b) Give two chemical properties of hydrogen chloride gas (c) State two uses of hydrogen chloride
Describe how sodium carbonate is used to remove water hardness
5g of calcium carbonate was strongly heated to a constant mass. Calculate the mass of the solid residue formed (Ca=40 0; C= 12.0; 0= 16.0). (2 marks)
During laboratory preparation of oxygen, manganese(IV) oxide is added to reagent H.
Figure 5 shows an apparatus used to separate a mixture of water and hexene.
A boiling tube filled with chlorine water was inverted in a trough containing the same solution and the set-up left in sunlight for about 2 hours.
Ethene is prepared in the laboratory by dehydration of ethanol.
The graph in Figure 4 was obtained when a certain substance was heated and its temperature recorded at regular intervals.
(a) State the purity of the substance. (I mark)
(b) Explain the answer in (a). (2 marks)
Calculate the mass of Zinc oxide that will just neutralize dilute nitric (V) acid containing 12.6 g of nitric (V) acid in water. (Zn = 65.0; O =16.0, H = 1.0, N = 14.0).
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?
(a) What is meant by lattice energy?
b) Study the energy level diagram below and answer the question that follows
What type of reaction is represented by the diagram?
ANSWERS
(a) Enthalpy change, when one mole of crystal lattice is broken into its ions in gaseous state.
(b) Endothermic reaction (process)
(a) Name the raw material from which sodium is extracted.
(b) Give a reason why sodium is extracted using electrolysis. (c) Give two uses of sodium metal.
ANSWERS
(a)Brine (NaCl)
(b) Sodium is very reactive (use electrolysis) More reactive than carbon. (c) Uses Sodium lamps, coolant in nuclear reactors Sodium cyanide, sodium amalgam Na202 , Extraction of titanium,
(a) Give the name of the first member of the alkene homologous series.
(b) Describe a chemical test that can be used to distinguish butanol from butanoic acid
a) Dissolving of potassium nitrate in water is an endothermic process. Explain the effect of increase in temperature on the solubility of potassium nitrate
b) The table below shows the solubilities of potassium sulphate and potassium chlorate (V) at different temperatures.
i) Draw the solubility curves for both salts on the same axis. (Temperature on the X-axis
ii)A solution of potassium sulphate contains 20g of the salt dissolved in 100 g of water at 100°C. This solution is allowed to cool to 25°C I) at what temperature will crystals first appears? II) What mass of crystals will be present at 25°C? iii) Which of the two salts is more soluble at 30°C? iv) Determine the concentration of potassium sulphate in moles per litre when the solubility of the two salts are the same (K= 39.0, O=16.0 ; S=32.0) v) 100 g of water at 100°C contains 19g of potassium sulphate and 19 g of potassium chlorate (V). Describe how a solid sample of potassium sulphate at 60°C can be obtained
The diagram below represents a set up of an electrolytic cell that can be used in the production of aluminium
(a) One the diagram, label the anode
(b) Write the equation for the reaction at the anode (c) Give a reason why the electrolytic process is not carried out below 950°C (d) Give a reason why the production of aluminium is not carried out using reduction process (e) Give two reasons why only the aluminium ions are discharged (f) State two properties of duralumin that makes it suitable for use in aircraft industry (g)Name two environmental effects caused by extraction of aluminium
(a) The scheme below shows some of the reaction of solution D. Study it and answer the questions that follow
(i) Give a possible caution present in solution D
(ii) Write an ionic equation for the reaction in Step II (iii) What observations would be made in Step V? Give a reason (iv) Explain why the total volume of hydrogen gas produced in step 1 was found to be very low although calcium and solution D were in excess. (v) State one use of substance E. (b)Starting with solid sodium chloride, describe how a pure sample of lead (II) Chloride can be prepared in the laboratory (c) (i) State a property of anhydrous calcium chloride which makes it suitable for use as a drying agent for chlorine gas. (ii) Name another substance that can be used to dry chlorine gas
(a) Other than temperature, state two factors that determine the rate of a chemical reaction.
(b) A solution of hydrogen peroxide was allowed to decompose and the oxygen gas given off collected. After 5 minute, substance G was added to the solution of hydrogen peroxide. The total volume of oxygen evolved was plotted against time as shown in the graph below
(i)Describe the procedure of determining the rate of the reaction at minute 12.
(ii)How does the production of oxygen in region AB compare with that in region BC? Explain (iii)Write an equation to show the decomposition of hydrogen peroxide. (c) Sulphur (IV) oxide react with oxygen to form Suplhur (VI) oxide as shown in the equation below
(ii)Name one catalyst used for the reaction.
(a) Draw the structures of the following.
(i)Butan -1-ol (ii)Hexanoic acid. (b) Study the flow chart below and answer the questions that follow
(i) State the conditions necessary for fermentation of glucose to take place
(ii) State one reagent that can be used to carry out process S. (iii) Identify gases P: T: (iv) How is sodium hydroxide kept dry during the reaction (v) Give one commercial use of process R. (c) When one mole of ethanol is completely burnt in air, 1370kJ of heat energy is released. Given that 1 lire of ethanol is 780 g , calculate the amount of heat energy released when 1 litre of ethanol is completely burnt (C = 12.0; H=1.0; 0=16.0) (d) State two uses of ethanol other than as an alcoholic drink.
(a) The grid below represents part of the periodic table . Study it and answer the questions that follow. The letters are not the actual symbols of the elements
i) Select the most reactive metal. Explain
ii) Select an element that can form an ion with a charge of 3- iii) Select an alkaline earth metal iv) Which group 1 element has the highest first ionization energy? Explain v) Element A combines with chlorine to form a chloride of A. State the most likely pH value of a solution of a chloride of A. Explain (b) (i) Explain why molten calcium chloride and magnesium chloride conduct electricity while carbon tetrachloride and silicon tetrachloride do not. (ii) Under the same conditions , gaseous neon was found to diffuse faster than gaseous fluorine. Explain this observation. (F=19.0;Ne=20.0) |
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