SCHJU – Chemistry COMMUNICATION 1. Calcium nitrate used in fireworks: Freshly made, both silver nitrate turns dark when exposed to sunlight. When solutions are clear and colorless, but has not labeled, imagine that someone precipitated with them. You do not want to wait for the silver nitrate solution to darken in order to identify the solutions. Name a chemical that can be used to precipitate a silver compound with the silver nitrate solution, but will produce no precipitate with the calcium nitrate solution. State the reason for your choice. (10 marks)
The Correct Answer and Explanation is:
To identify the silver nitrate solution without waiting for it to darken in sunlight, sodium chloride (NaCl) can be used as a chemical to precipitate the silver compound. When added to silver nitrate (AgNO₃) solution, sodium chloride will react with silver ions (Ag⁺) to form a white precipitate of silver chloride (AgCl), which is insoluble in water. However, no precipitate will form when sodium chloride is added to a calcium nitrate (Ca(NO₃)₂) solution, as calcium chloride (CaCl₂) is highly soluble in water and does not precipitate under normal conditions.
Reason for Choice:
- Precipitation of Silver Compounds: Silver ions (Ag⁺) readily react with chloride ions (Cl⁻) from sodium chloride to form silver chloride (AgCl), which is a white, insoluble precipitate. This is the key reaction used for detecting silver nitrate. The reaction can be written as: AgNO₃ (aq)+NaCl (aq)→AgCl (s)+NaNO₃ (aq)\text{AgNO₃ (aq)} + \text{NaCl (aq)} → \text{AgCl (s)} + \text{NaNO₃ (aq)}AgNO₃ (aq)+NaCl (aq)→AgCl (s)+NaNO₃ (aq)
- No Precipitation with Calcium Nitrate: When sodium chloride is added to calcium nitrate, the chloride ions will not precipitate any calcium compound because calcium chloride (CaCl₂) is soluble in water. Therefore, no precipitate forms, and this confirms the presence of calcium nitrate in the solution.
- Selectivity: Sodium chloride is effective in distinguishing between silver nitrate and calcium nitrate due to the solubility properties of the respective compounds. Silver chloride (AgCl) is insoluble in water, while calcium chloride (CaCl₂) is soluble. This selectivity makes sodium chloride an ideal choice for the precipitation test.
By performing this test, one can easily identify the silver nitrate solution based on the formation of a white precipitate and distinguish it from the calcium nitrate solution, which will show no change.
