(a) What is a chemical reaction ? Describe one activity each to show that a chemical change has occurred in…
(a) What is a chemical reaction ? Describe one activity each to show that a chemical change has occurred in which (i) change of colour, and (ii) change in temperature has taken place.
Solution
(a) A chemical reaction involves the breaking and making of bonds between atoms to produce new substances. / when reactant changes to products.
(i) Add lead nitrate solution to potassium iodide solution taken in a test tube. The colour changes from colourless solution to yellow ppt. /
Pb(NO3)2 + 2KI → PbI2 (Yellow) + 2KNO3
(Deduct ½ marks if colour is not mentioned in the reaction)
(or any example)
(ii) Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat. /
CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
(Quick lime) (Slaked lime)
(or any example)