KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Starting with barium nitrate solution, describe how a pure sample of barium carbonate can be prepared in the laboratory.
ANSWERS
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The graph below is a cooling curve for water. Study it and answer the questions that follow
(a) Explain what happens to the molecules of water in the region BC in terms of kinetic theory.
(b) In what state is the water in the region DE?
ANSWERS
The molecules of water are
(a) Loosing heat . The kinetic energy decreases and the molecules move closer to each other (b) Solid state
The table below is part of the periodic table. The letters are not the actual symbols of the elements. Study it and answer the questions that follows.
a) Select an element which is stored in paraffin in the laboratory
(b) How do the ionic radii of E and I compare? Explain
ANSWERS
(a) Element stored under paraffin G
(b) E is smaller than I. E has two energy levels while I has 3 energy levels.
Study the flow chart below and use it to answer the questions that follows
a) Name process T
b) Give the formula of W. c) State two uses of X
Describe how samples of lead (II) sulphate, ammonium chloride and sodium chloride can be obtained from a mixture of the three.
ANSWERS
Given that the E° of Cu(s) /Cu2+(aq) is +0.34 V and that of Zn (s)/Zn2+(aq) is —0.76 V, draw a labelled diagram of zinc and copper electrochemical cell. (3 marks)
During laboratory preparation of carbon(IV) oxide gas, dilute hydrochloric acid was added to substance L in a conical flask.
Study the information in Table 3 and use it to answer the questions that follow.
Use the information in Table 2 to answer the questions that follow.
(a) State what is meant by heat of reaction. (1 mark)
(b) Calculate the heat change when one mole of methane reacts completely with excess chlorine in the presence of UV light. (2 marks)
The heat of solution and hydration energy of potassium chloride is —17.2kJ and —689kJ respectively. Calculate the lattice energy of potassium chloride. (2 marks)
(a)Complete the following table. (2 marks)
(b) Explain why a solution of ammonia in methylbenzene has no effects on red litmus paper while in aqueous ammonia red litmus paper turns blue. (1 mark)
A crystal of iodine, heated gently in a test tube gave off a purple vapour.
(a) Write the formula of the substance responsible for the purple vapour. (b) What type of bond is broken when the iodine crystal is heated gently? (c) State one use of iodine.
ANSWERS
(a)Formula of Iodine I2
(b)Weak Van der Waals (c)Antiseptic
A radioactive substance weighing M kg took 1900 years for the original mass to reduce to 15 kg. Given that the half life of the radioactive substance is 380 years;
(a) Determine the original mass of the radioactive substance. (b) State two uses of radioactivity in medicine. .
Study the standard electrode potentials in the table below and answer the questions that follow.
(a) Which of the metals is the strongest reducing agent?
(b) What observations will be made if a silver coin was dropped into an aqueous solution of copper (II) sulphate? Explain.
ANSWERS
(a) Calcium
(b) No observable change silver is below copper in the reactivity series so it cannot displace it.
(a) One of the allotropes of sulphur is rhombic sulphur, name the other allotrope.
(b) Concentrated sulphuric (VI) acid reacts with ethanol and copper. State the property of the acid shown in each case. (i) Ethanol .................... (ii) Copper ....................
ANSWERS
(a) Monoclinic sulphur /Beta sulphur! Prismatic sulphur
(b) (i) Dehydrating property (ii) Oxidising property
The flow chart below shows various reactions of aluminium metal. Study it and answer the questions that follow
a) i) Other than water, name another reagent that could be R
ii) Write the formula of reagent Q b) Write an equation or the reaction in step 5.
Given the following substances: wood ash, lemon juice and sodium chloride.
(a) Name one commercial indicator that can be used to show whether wood ash, lemon juice and sodium chloride are acidic, basic or neutral. b) Classify the substances in 15(a) above as acids, bases or neutral
ANSWERS
(a) Universal indicator / litmus paper
(b) Acid, base, neutral.
The table below shows behaviour of metals R, X, Y and Z. Study it and answer the questions that follow:
a) Arrange the metals in the order of reactivity starting with the most reactive
b) Name a metal which is likely to be i X ii Y
ANSWERS
(a) Reactivity series starting with the most reactive
X R Z Y (b) X could be potassium Y could be copper
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
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 |
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