K.C.S.E Chemistry Q & A - MODEL 2007.PP2.QN.6

14/10/2020

KCSE Chemistry 2007 Topical Questions and Answers

All Questions Featuring Chemistry Form 1, Form 2, Form 3, Form 4, Paper 1, Paper 2 and Paper 3

(a) The elements nitrogen, phosphorous and potassium are essential for plant growth.
(i) Potassium in fertilizers may be in the form of potassium nitrate Describe how a sample of a fertilizer may be tested to find out if it contained nitrate ions.
(ii) Calculate the mass of nitrogen present if a 25kg bag contained pure ammonium phosphate, (NH₄)₂ HPO₄. (N = 14.0, H=1.0, P = 31.0, O = 16.0
(b) The table below shows the solubility of ammonium phosphate in water at different temperatures.

(i) On the grid provided, draw the solubility curve of ammonium phosphate (Temperature on x – axis)
(ii) Using the graph, determine the solubility of ammonium phosphate at 25°C
(iii) 100g of a saturated solution of ammonium phosphate was prepared at 25°C
I what is meant by a saturated solution?
II Calculate the mass of ammonium phosphate which was used to prepare the saturated solution
(c) The graph below shows how the PH value of soil in a farm changed over a period of time

(i) Describe how the pH of the soil can be determined
(ii) State one factor that may have been responsible for the change in the soil pH in the time interval AB

ANSWERS