Required Practical 8: Water

Potable vs Pure Water

• Potable water = safe to drink.

• Pure water = contains no dissolved solids and has a pH of 7.

• Potable water:

  • Often contains dissolved solids.

  • pH may not be 7.

Testing a Water Sample for Purity

1. Check the pH:

   • Place a small amount of water on universal indicator paper.

   • Universal Indicator is green is pH = 7

   • pH = 7 → neutral.

   • If pH ≠ 7 → contains dissolved acids/alkalis → not pure.

2. Check for dissolved solids:

   • Weigh an empty evaporating basin.

   • Add water sample, heat gently with a Bunsen burner until all water evaporates.

   • Allow basin to cool, reweigh.

   • If mass increases → dissolved solids were present (not pure).

   • If mass unchanged → no dissolved solids (could be pure, but may still contain gases).

Purifying Water by Distillation

Apparatus:

• Conical flask with water sample, tripod & gauze.

• Delivery tube leading to test tube in a beaker of ice + water.

Method:

1. Heat water gently until it boils.

2. Water evaporates → forms steam (water vapor).

3. Vapor travels through delivery tube.

4. Steam condenses in the cold test tube → distilled water.

Result:

• Distilled water = pure water.

• Contains no dissolved solids.

• pH = 7.

✅ Key Idea:

• Pure water = no dissolved solids, neutral pH.

• Potable water = safe to drink but may contain dissolved substances.

• Distillation produces pure water by separating water from dissolved solids.