Question

Geetika poured $ 20{\text{ g}} $ of salt into $ 200 {\text{mL}} $ of water in a beaker. She stirred the water to dissolve the salt completely. Then she heated the solution until it reduced to half.
How many grams of salt can be recovered from the remaining solution?

(A) 0g
(B) 10g
(C) 20g
(D) 40g

Answer 1

Hint: Generally, evaporation can be described as a process by which a liquid or solid is converted into vapour. The method in which a liquid state of matter is converted into a gaseous state of matter is evaporation. The rate of evaporation increases as the temperature increases.

Complete Step-by-Step solution:
It is provided in the question that Geetika poured $ 20{\text{ g}} $ of salt into $ 200 {\text{mL}} $ of water in a beaker. Later, she stirred the water in the beaker so that the salt inside the water dissolved completely. Then it is said that Geetika boiled the beaker until its volume gets reduced to half.
Evaporation occurs when a liquid material becomes a gas. As the water is hot, it evaporates. The molecules move and vibrate so quickly that they dissipate into the atmosphere as water vapor molecules.
In this case, half of the water inside the beaker evaporated and half of the water is still left inside the beaker. Also, only water has evaporated and no amount of the salt added in the water evaporates.
If salt would have been evaporated, then the food we eat would have been tasteless. Also, the ocean water would not be saline. But this is not the case here.
The salt that Geetika added never evaporated. Only the water inside the beaker evaporated. This also means that the amount of salt before and after evaporation remains the same, that is, $ 20{\text{ g}} $ .
Hence, the correct option is (C).

Note:
Evaporation is a form of vaporization that usually takes place on the surface of liquids and involves the transition into the gaseous phase of the liquid particles. Therefore, it is said that this process involves a change in the liquid state of matter.