Write the chemical equation of the reaction with an example each in which the following change has taken place:(i) Change in colour(ii) Change in temperature (iii) Formation of precipitate.
Question
Write the chemical equation of the reaction with an example each in which the following change has taken place:(i) Change in colour(ii) Change in temperature (iii) Formation of precipitate.
Solution
(i) Change in colour:
The reaction between potassium iodide (KI) and lead nitrate (Pb(NO3)2) results in a change in colour. The reaction is as follows:
2KI(aq) + Pb(NO3)2(aq) → 2KNO3(aq) + PbI2(s)
In this reaction, the yellow precipitate of lead iodide (PbI2) indicates a change in colour.
(ii) Change in temperature:
The reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) is exothermic and results in a change in temperature. The reaction is as follows:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
In this reaction, heat is released causing the temperature of the solution to increase.
(iii) Formation of precipitate:
The reaction between barium chloride (BaCl2) and sodium sulphate (Na2SO4) results in the formation of a precipitate. The reaction is as follows:
BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s)
In this reaction, the white precipitate of barium sulphate (BaSO4) is formed.
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