KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
(a) The diagram below represents part of the structure of a sodium chloride crystal.
The position of one of the sodium ions in the crystal is shown as (i) On the diagram, mark the position of the other three sodium ions (ii) The melting and boiling points of sodium chloride are 801°C and 1413°C respectively. Explain why sodium chloride does not conduct electricity at 25°C, but does so at temperatures between 801° C and 1413°C (b) Give a reason why ammonia gas is highly soluble in water (c) The structure of an ammonia ion is shown below:
Name the type of bond represented in the diagram by N → H
(d) Carbon exists in different crystalline forms. Some of these forms were recently discovered in soot and are called fullerenes (i) What name is given to different crystalline forms of the same element? (ii) Fullerenes dissolve in methylbenzene while the other forms of carbon do not. Given that soot is a mixture of fullerenes and other solid forms of carbon, describe how crystals of fullerenes can be obtained from soot. (iii) The relative molecular mass of one of the fullerenes is 720. What is the molecular formula of this fullerene? (C=12.0)
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(a) Study the information below and answer the questions that follow:
The letters do not represent the actual symbols of the elements
An element Y has the electronic configuration 2.8.5
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(a) Metallic bonding
(b) Group 1 Each atom contains one electron in its outer most energy level
Starting with sodium metal, describe how a sample of crystals of sodium hydrogen carbonate may be prepared.
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a)Dilute Nitric acid
b)Silver metal c)oxygen
Explain why there is general increase in the first ionization energies of the elements in period 3 of the periodic table from left to right.
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Both chlorine and iodine are halogens.
a) What are halogens? b) In terms of structure and bonding, explain why the boiling point of chlorine is lower than that of iodine.
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(a) Group (VIII) elements
(b) Chlorine molecule is smaller and the strength of Vander Waals forces between molecules of chlorine is weak as compared to iodine.
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(a) Carbon (IV) oxide
(b) Blue flame, carbon (II) oxide is burning
a) Distinguish between isotopes and allotropes.
b) The chart below is 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 element in period three which has the shortest atomic radius. Give a reason for you answer.
ii) Element F has the electronic structure, 2.8.18.4 on the chart above, indicate the position of element F. iii) State one use of the elements of which E is a member. iv) Write an equation to show the action of heat on the nitrate of element C. c) When 3 litres of chlorine gas were completely reacted with element D, 11.875g of the product were formed. Determine the relative atomic mass of element D. (Atomic mass of chlorine = 35.5; molar gas volume = 24litres)
The diagram below represents part of a set – up used to prepare and collect gas T.
a) Name two reagents that are reacted to produce both carbon (IV) oxide and carbon(II) oxide.
b) Write the equation for the reaction which takes place in the wash bottles. c) Give a reason why carbon(II) oxide is not easily detected.
a) Distinguish between a covalent bond and a co-ordinate bond
b) Draw a diagram to show bonding in an ammonium ion.
The table below shows the relative atomic masses and the percentage abundance of the isotopes L1 of element L.
The atomic numbers of elements C and D are 19 and 9 respectively. State and explain the electrical conductivity of the compound CD in:
(a) Solid state (b) aqueous state.
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Using dots (.)and crosses (x) to represent outermost electrons, draw diagrams to show the bonding in CO2 and H3O+ (Atomic numbers; H = 1.0,C= 14.0, O = 8 ).
When extinguishing a fire caused by burning kerosene, carbon dioxide is used in preference to water .Explain
Expected Response
- Kerosene floats on water therefore it continues to burn
- Carbon dioxide blanket covers the flame OR cuts off the supply of oxygen
(a) An atom Q can be represented as
What does the number 52 represent?
(b) Study the information in the table below and answer the equations that follow (Letters are not the actual symbols of the elements)
(i) Write the formula of the compound formed when N reacts with P. (atomic numbers are N = 20; P = 17)
(ii) Identify the elements which belong to the third period of the periodic table. Explain (iii) Which of the element identified in b (ii) above comes first in the third period? Explain (iv) Select two elements which are non- metals (c) The table below gives some properties of substances I, II, III, and IV. Study it and answer the questions that follow
(i) What type of bonding exists in substances I and II
I II (ii) Which substances is likely to be sulphur? Explain
Dry carbon monoxide gas reacts with heated lead (II) oxide as shown in the equation below
PbO(s) + CO(g) →Pb (s) + CO2 (g) (a) Name the process undergone by the lead (II) oxide (b) Give a reason for your answer in (a) above (c) Name another gas that can be used to perform the same function as carbon monoxide gas in the above reaction.
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Study the table below and answer the questions that follow:
a) Complete the table by filling in this missing atomic numbers and atomic mass. (2mks) b) Write the electron arrangement for the following ions (2mks) Ca+ P3+ c) What is the melting point of hydrogen in degrees Kelvin? (1mk) d) Which of the allotropes of phosphorous ha a higher density? Explain (2mks) e) The mass numbers of three isotopes of magnesium are 24, 25 and 26. What is the mass number of the most abundant isotope of magnesium? Explain (2mks) f) Give the formula of the compound formed between aluminium and carbon.(1mks) g) Explain the difference in the melting points of magnesium and sodium.(2mks)
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In terms of structure and bonding, explain why graphite is used as a lubricant.
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