Chemistry – Chemistry of the environment - Water | e-Consult

To assess the purity of water using melting and boiling point, a student would follow these steps:

Melting Point Test:

• Apparatus: Melting point apparatus (including a melting point tube, thermometer, clamp, and stand), a water sample, and a weighing balance.
• Procedure:

  • Accurately weigh a small amount of the water sample into the melting point tube.
  • Clamp the melting point tube in the melting point apparatus.
  • Slowly heat the water sample, observing the temperature.
  • Record the temperature at which the water begins to melt and the temperature at which it is completely melted.

• Interpretation: Pure water has a sharp melting point of 0°C. Impurities will depress and broaden the melting point range. A depressed melting point indicates the presence of dissolved substances. The extent of depression is related to the amount of impurity. A broad melting point range suggests significant impurities.

Boiling Point Test:

• Apparatus: A boiling tube, a thermometer, a Bunsen burner, a tripod, and a wire gauze.
• Procedure:

  • Set up the boiling tube in the water bath using a tripod and wire gauze.
  • Heat the water sample gently.
  • Monitor the temperature of the boiling water using the thermometer.
  • Record the temperature at which the water starts to boil and the temperature at which it is boiling steadily.

• Interpretation: Pure water boils at 100°C at standard atmospheric pressure. Impurities will raise the boiling point. The boiling point will be higher than 100°C, and the boiling point depression will be proportional to the concentration of the impurities. A significant deviation from 100°C indicates the presence of dissolved substances.