KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
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Using dots (.) and crosses(x) to represent electrons, show bonding in the compounds formed when the following elements react: (si = 14, Na = 11 and Cl = 17)
a) Sodium and chlorine b) Silicon and chlorine
a) The set-up below was used to collect gas F, produced by the reaction between water and calcium metal.
(i) Name gas F
(ii) At the end of the experiment, the solution in the beaker was found to be a weak base. Explain why the solution is a weak base. (iii) Give one laboratory use of the solution formed in a beaker. (b) The scheme below shows some reactions starting with calcium oxide. Study it and answer the questions that follow.
(i) Name the reagents used in steps 2 and 4
Step 2 ………. Step 4 ………. (ii) write an equation for the reaction in step 3. (iii) Describe how a solid sample of anhydrous calcium sulphate is obtained in Step 5
Carbon dioxide can be dissolved in water under pressure to make an acidic solution.
a) What is meant by an acidic solutions? b) aqueous lead (II) nitrate reacts with the acidic solution to form a precipitate. Write anionic equation for the reaction.
Four metal F,G,H and J were each separately added to cold water, and steam. The table below is a summary of the observations made and the formulae of the hydroxides formed.
a) Which two elements are likely to be in the same group of the periodic table?
b) Arrange the metals in the order of their reactivity starting with the most reactive
answers
Both diamond and graphite have giant atomic structures. Explain why diamond is hard while graphite is soft.
Answer
answer
The table below gives the atomic numbers of elements W, X, Y, and Z. The letters do not represent the actual symbols of the elements. a) Which one of the elements is least reactive? Explain (1mk) b) i) Which two elements would react most vigorously with each other? (1mk) ii) Give the formula of the compound formed when the elements in b(i) react (1mk)
expected response
a) X, both energy levels are full i.e 2:8 outer energy level full/has octane structure/inert gas structure.
b) (i) W and Y (ii) YW
expected response
Number of neutrons =1
Number of electrons=1
a) The chart below is an outline of part of the periodic table.
With the help of vertical and horizontal lines, indicate the direction of increasing metallic nature of the elements.
Which types of elements are represented in the shaded area? b) i) Element A is the same group of the periodic table as chlorine. Write the formula of the compound formed when A reacts with potassium metal. ii) What type of bonding exists in the compound formed in (b) (l) above? Give a reason for your answers. c) Starting with aqueous magnesium sulphate, describe how you would obtain a sample of magnesium oxide. d) Write two ionic equations to show that aluminum hydroxide is amphoteric
Explain why the reactivity of group (VII) elements decreases down the group
answer
Yellow phosphorous reacts with chlorine gas to form a yellow liquid. The liquid fumes when exposed to air. Explain these observations
answer
An oxide of element F has the formula F2O5
(a) Determine the oxidation state of F (b) In which group of the periodic- table is element F
Some sodium chloride was found to be contaminated with copper (ll) oxide.
Describe how a sample of sodium chloride can be separated from the mixture
ANSWER
expected response
6.
a) G b) E
Describe how a solid sample of Zin (II) carbonate can be prepared starting with zinc oxide
With reference to iodine, distinguish between covalent bonds and Van Der Waals forces
answers
When carbon dioxide gas was passed through aqueous calcium hydroxide a white suspension was formed
(a) Write an equation for the reaction that took place (b) State and explain the changes that would occur when carbon dioxide gas is bubbled through the white suspension
When potassium nitrate is heated, it produces potassium nitrate and gas C
(a) Identify gas C (b) Name the type of reaction undergone by the potassium nitrate
answer
(a) Write the electronic configuration of calcium ( atomic number 20 ) and beryllium (atomic number 4)
(b) Why is calcium more reactive than beryllium
answers
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