Analytical chemists are trying to determine the identity of an unknown substance

Question

Analytical chemists are trying to determine the identity of an unknown substance. They have narrowed it down to two possibilities, silver nitrate or potassium nitrate. You have been assigned the task of determining how to finish testing the solution to reveal its identity. Use your knowledge of double displacement reactions, and the solubility table to come up with a laboratory procedure which will identify the unknown solution. Be sure to include a purpose, hypothesis, materials, and procedure.

Explanation / Answer

Purpose: To find out whether the given solution contains silver nitrate or potassium nitrate.

Hypothesis: Double displacement reactions

Treatment of silver nitrate with base gives dark grey silver oxide:

2 AgNO3 + 2 NaOH %u2192 Ag2O + 2 NaNO3 + H2O

However KNO3 being formed by the reaction of a strong base and a strong acid does not exhibit the above reaction.

Thus, if KNO3 is present, dark grey precipitate is not observed

Materials required: Beakers, Given solution, Sodium hydroxide, stirrer

Procedure:

1. Pour 300ml of sodium hydroxide in a beaker

2. Take the given solution and pour it into the beaker with NaOH

3. Stir for sometime.

4. If dark grey precipitate is obseved, then the solution is Silver nitrate

%. Otherwise the solution is Potassium nitrate

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