Question

How would you confirm that a colorless liquid given to you is pure water?

Answer 1

To confirm that a colorless liquid is pure water, you can use the following tests:

1. Boiling Point Test:

Procedure: Heat the liquid in a clean beaker and observe the temperature at which it boils.

Observation: Pure water boils at 100°C (at 1 atm pressure). If the liquid boils at this temperature, it may be pure water.

Note: Impurities in water (e.g., salts, minerals) will raise the boiling point, so if the boiling point is higher, the liquid may not be pure water.

2. Freezing Point Test:

Procedure: Place the liquid in a freezer and observe the temperature at which it freezes.

Observation: Pure water freezes at 0°C. If the liquid freezes at this temperature, it is likely pure water.

Note: Impurities can lower the freezing point, so if the liquid freezes at a temperature lower than 0°C, it’s not pure water.

3. Electrical Conductivity Test:

Procedure: Place two electrodes in the liquid and connect them to a simple circuit with a power source (e.g., a battery) and a light bulb.

Observation: Pure water is a poor conductor of electricity. If the light bulb doesn't glow, it indicates that the liquid is likely pure water.

Note: Water containing dissolved salts, minerals, or other ions will conduct electricity better, causing the light bulb to glow.

4. Taste Test (Not Recommended for Safety):

Observation: Pure water should have a neutral taste with no flavor. Any unusual taste could indicate that the liquid contains impurities.

Note: This test should only be done with caution, as some chemicals may be harmful even if they appear colorless.

5. pH Test:

Procedure: Use pH paper or a pH meter to measure the acidity or alkalinity of the liquid.

Observation: Pure water has a neutral pH of 7 at 25°C. If the liquid has a pH significantly different from 7, it is not pure water.

6. Evaporation Test:

Procedure: Place a small amount of the liquid in a clean, shallow dish and allow it to evaporate.

Observation: Pure water should evaporate completely, leaving no residue behind. If there is any residue, the liquid contains dissolved substances, indicating it is not pure water.

Conclusion:

If the liquid passes the tests for boiling point, freezing point, pH, electrical conductivity, and leaves no residue upon evaporation, then you can confirm it is pure water.