KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Starting with zinc sulphate solution, describe how a sample of zinc oxide can be obtained
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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.
An atom of element A has mass number 39 and 19 protons.
Explain why hydrogen forms compounds in which its oxidation state is either + 1 or -1 (Atomic number of hydrogen is 1)
The table below shows the properties of substances K,L,M and N
Select the substances which are likely to be:
a) Copper metal b) Magnesium chloride
Expected Response
(a) Copper metal M
(b) Magnesium chloride K The melting point of phosphorous dichloride is – 910C. While that of magnesium chloride is 7150C.In terms of structure and bonding, explain the difference in their melting points.
Expected Response
A student investigated the effect of an electric current by passing it through some substances.
The student used inert electrodes, and connected a bulb to the circuit. The table below shows the substances used and their states.
a) In which experiments did the bulb not light?
b) Explain your answer in (a) above.
By using aqueous sodium chloride, describe how a student can distinguish calcium ions from lead ions.
The plots below were obtained when the atomic radii of some elements in groups I and II were plotted against atomic numbers.
Explain:
a) The trend shown by Li, Na and K. b) Why the atomic radii of elements Be, Mg, and Ca are lower than those of Li, Na and K.
ANSWERS
(a)The atomic radii increase with increase in atomic number. This is due to increase in energy levels.
(b) The group II elements have more protons than group I elements hence this increases the nuclear attraction for the outer electrons.
(a) Diamond and graphite are allotropes of carbon. What is meant by an allotrope?
(b) Explain why graphite can be used as a lubricant while diamond cannot.
ANSWERS
(a) These are different forms carbon in the same physical state.
(b) The hexagonal graphite rings have weak Van der Waals forces between the layers that allow the layers to slide over each other , while in diamond the atoms are held by strong Covalent bonds.
The information in the table below relates to elements in the same group of the periodic table. Study it and answer the question that follows:
Which element has the highest ionization energy? Give reason.
Expected Answer
G3, because it has the smallest atomic radius. Its outer most electron is tightly held by the nucleus or it requires a lot of energy to remove it.
The diagram below illustrates a method of preparing salts by direct synthesis
(a) This method can be used to prepare either aluminum chloride or iron (III) chloride.
Explain why it cannot be used to prepare sodium chloride. (b) Describe how a sample of sodium chloride can be prepared in the laboratory by direct synthesis.
ANSWERS
(a) It does not sublime.
(b) Cut a piece of Sodium metal, place it on a deflagrating spoon. heat it briefly then lower it into a gas jar of chlorine. It will continue burning forming Sodium Chloride.
In terms of structure and bonding, explain the following observations:
(a) The melting point of aluminum is higher than that of sodium (b) Melting point of chlorine is lower than that of sulphur
ANSWERS
(a) Aluminium has a stronger metallic bond because it has more delocalised electronsthan sodium.
(b) Sulphur has a ringed structure of S8 molecules whiles chlorine is diatomic. The forces in sulphur are stronger than chlorine.
Write equations to show the effect of heat on each of the following:
(a) Sodium hydrogen carbonate (b) Silver nitrate (c) Anhydrous iron (II) sulphate
The grid below is part of the periodic table. Use it to answer the questions that follow. (The letters are not the actual symbols of the elements)
a) Which is the most reactive non-metallic element shown in the table? Explain.
b) i) Write the formula of the compound formed when element A reacts with element B. ii) Name the bond type in the compound formed in b (i) above. c) i) What is the name given to the group of elements where C, G and H belong? ii) Write an equation for the reaction that occurs when C in gaseous form is passed through a solution containing ions of element H. d) The melting points of elements F and G are 1410°C and -101°C respectively. In terms of structure and bonding, explain why there is a large difference in the melting points of F and G. e) D forms two oxides. Write the formula of each of the two oxides. f) J is an element that belongs to the 3rd period of the periodic table and a member of the alkaline earth elements. Show the position of J in the grid.
How would you obtain a sample of pure iodine from a mixture of iodine and lead sulphate?
Expected Response
Heat the mixture iodine sublimes and can be collected from the cool part of the test tube.
(a) The electronic arrangement of the ion of element Q is 2.8.8. If the formula of the ion is Q3-,state the group and period to which Q belongs.
Group: Period: (b) Helium, neon and argon belong to group 8 of the periodic table. Give: (i) the general name of these elements; (ii) one use of these elements.
Give a reason why phosphorus is stored under water.
Expected Response
To keep away air/ oxygen which would react with it
The electronic structures for elements represented by letters A,B,C,D are
A=2 .8.6 B 2.8.2 C 2. 8. 1 D 2. 8. 8. a) Select the element which forms:
Use the following information on substances S, T, V and hydrogen to answer the questions that follow:
(i) T displaces V from a solution containing V ions. (ii) Hydrogen reacts with the heated oxide of S but has no effect on heated oxide of V. (a) Arrange substances S, T, V and hydrogen in the order of increasing reactivity. (b) If T and V are divalent metals, write an ionic equation for the reaction in (i) above.
Distinguish between ionisation energy and electron affinity of an element.
ANSWERS
(a) The grid given below represents part of the periodic table. Study it and answer the questions that follow. (the letters do not represents the actual symbol of the elements)
(b) Study the information in the table below and answer the questions that follow (the letters do not represent the actual symbol of the substances)
II. By downward displacement of air? (Density of air is 1.29 x 10-3g/cm3 at room temperature. Related Chemistry Questions and Answers on Chemical Families Form 2 Level
Compound Q is a solid with a giant ionic structure. In what form would the compound conduct an electric current
Expected Response
16. When dissolves in water or fused / molten state
Use the scheme below to answer the questions that follow
(a) Identify the solid
H J (b) State one commercial use of solid J |
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