​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.

• black mass will be seen 

• Turn from blue to white 

• Dehydration

​An experiment was carried out to prepare crystals of magnesium sulphate. Excess magnesium powder was added to 100 cm3 of dilute sulphuric (VI) acid in a beaker and warmed until no further reaction took place. The mixture was filtered and the filtrate evaporated to saturation, then left to cool for crystals to form.
(a) (i) Write an equation for the reaction. 
(ii) Explain why excess magnesium powder was used. 
(iii) State how completion of the reaction was determined. 
(iv) What is meant by a saturated solution? 
(v) Explain why the filtrate was not evaporated to dryness. 
(b) When bleaching powder, CaOCl2, is treated with dilute nitric(V) acid, chlorine gas is released. This reaction can be used to determine the chlorine content of various samples of bleaching powders and liquids.
(i) Write an equation for the reaction of nitric(V) acid with bleaching powder.
(ii) Calculate the volume of chlorine produced when 10g of CaOCl2 is treated with excess nitric (v) acid. (Ca = 40.0; 0 = 16.0; Cl = 35.5; 1 mole of gas occupies 22.4dm3 at s.t.p) 
(c) Apart from use of chlorine gas in bleaches and water treatment, state two other uses of chlorine gas.

 You are provided with solid potassium hydrogen carbonate. Describe how a solid sample of  potassium nitrate can be prepared.

 Study the flow chart in Figure 1 and answer the questions that follow.

Gas N forms a while suspension with aqueous calcium hydroxide.
(a) Name the anion present in the potassium salt. 
(b) Write an ionic equation for the formation of solid M. 
(c) Give one use of gas N.

(a) Define a soluble base. 
(b) Aqueous solutions of 2M ethanoic acid and 2M nitric(V) acid were tested for electrical conductivity. Which solution is a better conductor of electricity? Explain.

The following steps were used to analyse a metal ore.
(i) An ore of a metal was roasted in a stream of oxygen. A gas with a pungent smell was formed which turned acidified potassium dichromate(VI) green.
(ii) The residue left after roasting was dissolved in hot dilute nitric(V) acid. Crystals were obtained from the solution.
(iii) Some crystals were dried and heated. A brown acidic gas and a colourless gas were evolved and a yellow solid remained. (iv) The solid was yellow when cold.
(v) The yellow solid was heated with powered charcoal. Shiny beads were formed.
Name the:
(a) gas formed when the ore was roasted in air. 
(b) gases evolved when crystals in step (iii) were heated. 
(c) yellow solid formed in step (iii). 
(d) shiny beads in step (iv). 
(e) The yellow solid from procedure (iii) was separated, dried, melted and the melt electrolysed using graphite electrodes.
I. Describe the observations made at each electrode. 
II. Write the equation for the reaction that took place at the anode. 
(f) Some crystals formed in step (ii) were dissolved in water, and a portion of it reacted with potassium iodide solution. A yellow precipitate was formed. Write an ionic equation for this reaction. 
(g) To another portion of the solution from (f), sodium hydroxide solution was added drop by drop until there was no further change. Describe the observation made. 
(h) To a further portion of the solution from (f), a piece of zinc foil was added.
I. Name the type of reaction taking place. 
II. Write an ionic equation for the above reaction.

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. 

​Starting with copper, describe how a pure sample of copper(II) carbonate can be prepared.

Copper(II) ions react with excess aqueous ammonia to form a complex ion.
(a) (i) Write an equation for the reaction that forms the complex ion. 
(ii) Name the complex ion. 
(b) Explain why CH4 is not acidic while HCl is acidic yet both compounds contain hydrogen. 

A sample of water is suspected to contain sulphate ions. Describe an experiment that can be carried out to determine the presence of sulphate ions. 

A compound whose general formula is M(OH)3 reacts as shown by the equation below.

​(a) What name is given to compounds which behave like M(OH) 3 in the two reactions.
(b) Name two elements whose hydroxides behave like that of M.