Precipitation Reaction

Chemistry report

precipitation reactions

Purpose

To observe and then explain various precipitation reactions.

Theory

If one dissolves various salts in water, new salt combinations become possible. The positive metal ion in one salt solution combines with the negative ion in the other. But ions of the same charge cannot be together for they repel each other. If one of these salts is insoluble, then it will precipitate from the solution.

The general formula for a precipitation reaction is:

AB (aq) + XY (aq) -----> AY (s) + XB (aq)

For example, when we mix together potassium iodide solution and lead(II) nitrate solution, a precipitate of lead(II) iodide forms. We can write it in chemical equation and ionic equation. Ionic equation is the equation which shows only ions that form precipitate (or the other salts that are insoluble).

Chemical equation: Pb(NO3)2 (aq) + 2KI (aq) ( PbI2 (s) + 2KNO3 (aq)

Ionic equation: Pb2+ (aq) + 2I- (aq) ( PbI2 (s)

Materials

Test tubes

Test tubes holder

Droppers

Chemicals

demineralized water

0.1 M solutions of

- Silver nitrate

- Manganese(II) nitrate

- Iron(III) nitrate

- Sodium sulfide

- Sodium chloride

- Sodium phosphate

Methods

1. Rinse test tubes with demineralized water to avoid experimental error.

2. Prepare all the material and set test tubes on the test tubes holder.

3. Mix 1 ml of each solution together in pairs so all combinations is tasted.

4. See how each combination is in color and if it precipitates.

Results

|Solution |Silver nitrate |Manganese(II) nitrate |Iron(III) nitrate |

| | |Slightly turbid white solution | |

|Sodium sulfide |Black precipitate. |with white precipitate. |Brown solution. |

|...