​These are chemistry questions and answers categorized according to topics, papers i.e. Paper 1 and 2, Levels i.e. form 1 to form 4, kcse year the examination was done and section A or B
Select topic/category to open topical questions from that particular option provided.

 Explain why a solution of sodium chloride Conducts electricity while that of sugar does not.

W is a colourless aqueous solution with the following properties:

• I It turns blue litmus paper red.
• II On addition of cleaned magnesium ribbon, it gives off a gas that burns with a pop sound.
• III On addition of powered sodium carbonate, it gives off a gas which forms a precipitate with calcium hydroxide solution.
• IV When warmed with copper(II) oxide powder, a blue solution is obtained but no gas is given off
• V On addition of aqueous barium chloride, a white precipitate is obtained.

(a) (i) State what properties (I) and (III) indicate about the nature of W. 
(ii) Give the identity of W. 
(iii) Name the colourless solution formed in (II) and (III). 
(iv) Write an ionic equation for the reaction indicated in (V).
(b) Element V conducts electricity and melts at 933K. When chlorine gas is passed over heated V, it forms a vapour that solidifies on cooling. The solid chloride dissolves in water to form an acidic
solution. The chloride vapour has a relative molecular mass of 267 and contains 19.75% of V. At a higher temperature, it dissociates to a compound of relative molecular mass 133.5. When aqueous
sodium hydroxide is added to the aqueous solution of the chloride, a white precipitate is formed which dissolves in excess alkali. (V = 27.0 ; CI = 35.5)
(i) Determine the:

• I empirical formula 
• II molecular formula 

(ii) Draw the structure of the chloride vapour and label the bonds. 
(iii) Write an equation for the reaction that form a white precipitate with sodium hydroxide. 

In terms of structure and bonding, explain why graphite is used as a lubricant in machines.

​The atomic numbers of some elements P, Q, R and S are 6, 8, 12 and 17 respectively.
(a) Draw the dot (•) and cross (X) diagrams for the compounds formed when:
(i) R and Q react 
(ii) P and S react. 
(b) Explain why the melting point of the compound formed by P and S is lower than that formed by R and Q.

Table 1 shows the atomic numbers and the first ionisation energies of three elements. The letters are not actual symbols of the elements. Use it to answer the questions that follow.

​(a) Explain the trend in first ionisation energy from A to C. 
(b) Write the electronic configuration for the ion of C. 

(a) Write an equation to show the effect of heat on the nitrate of: 
(i) Potassium
(ii) Silver
(b) The table below gives information about elements Ai, A2, A3, and A4
i) In which period of the periodic table is element A2? Give a reason.

(ii) Explain why the atomic radius of:
I. Ai is greater than that of A2;
II. A4 is smaller than its ionic radius.
(iii) Select the element which is in the same group as A3.
(iv) Using dots (•) and crosses(x) to represent outermost electrons, draw a diagramto show the bonding in the compound formed when Ai reacts with A4. 

​Use the information in the table below to answer the questions that follow. The letters do not represent the actual symbols of the elements.

​(a) Give reasons why the melting point of:
(i) S is higher than that of R; 
(ii) V is lower than that of U. 
(b) How does the reactivity of W with Chlorine compare with that of R with chlorine? 
Explain.
(c) Write an equation for the reaction between T and excess oxygen.
(d) When 1.15g of R were reacted with water, 600cm3 of gas was produced.
Determine the relative atomic mass of R. (Molar gas volume = 24 000 cm3).
(e) Give one use of element V.

Aluminium is both malleable and ductile.
(a)What is meant by?
(i) Malleable:
(ii)Ductile
(b)State One use of aluminium based on:
(i)malleability
(ii)ductility

(a) Name the method that can be used to obtain pure iron (III) chloride from a mixture of iron (III) chloride and sodium chloride. 
(b) A student was provided with a mixture of sunflower flour, common salt and a red dye. The characteristics of the three substances in the mixture are given in the table below.

The student was provided with ethanol and any other materials needed.
Described how the student can separate the mixture into its three components
c) The diagram below show part of a periodic table. The letters do no represent the actual symbols of elements. Use the diagram to answer the questions that follow.

i) Explain why the oxidizing power of W is more than that of X 
ii) How do the melting points of R and T compare? Explain 
iii) Sketch an element that could be used
i) In weather ballons 
ii) For making a cooking pot 
d i) Classify the substances water, iodine, diamond and candle wax into elements and compounds

​ii) Give one use of diamond

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.

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

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.

​Table 1 shows the properties of two chlorides, D and E.

(a) State the type of bond present in:

• (i)  D (1 Mark)
• (ii) E (1 mark)

(b) Explain in terms of structure and bonding, the difference in electrical conductivity of the chlorides D and E. (1 mark)

Given that the atomic number of Y is 13 and that of Z is 9:
a)Write the electronic arrangement of Y and Z; 
b) Draw the dot (.) and cross(x) diagram for the compound formed by Y and Z