Question

Megha was told to observe an experiment and note down its details. This is what she wrote
A jar of clear water was put on the boil. The steam was allowed to escape. When the volume of water became almost half its original volume, the gas was switched off.
When the water cooled down to room temperature, a powdery substance whitish in colour was seen stuck to its sides.
Megha was told to
(1) To name the process from the mileu of names:- galvanization, precipitation , sublimation, corrosion, evaporation.
(2) To name the powdery substance.
(3) To explain why this powdery substance formed.
(4) What kind of change could this be? [2 MARKS]

Answer 1

Reason out: 0.5 Marks each.

1. Evaporation
2. A salt of either Calcium or Magnesium which are commonly found in dissolved states in water rendering it hard.
3. This powdery substance formed due to the presence of dissolved salts of either Sodium, Potassium , Calcium . These are generally termed as contaminants.
4. Evaporation is a physical change, as if the water vapour is allowed to be cooled, its physical state changes back to liquid form that is water. The powdery substance can be restirred back to make a solution.