Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Evaporation: The process of conversion of a liquid into its vapor state at any temperature below its boiling point. It is used to separate a soluble solid from a liquid solvent, such as obtaining salt from seawater.
Condensation: The process of conversion of water vapor into its liquid form on cooling. For example, water droplets forming on the outer surface of a glass containing ice-cold water.
The process of evaporation takes place continuously wherever water () is present and is accelerated by an increase in temperature or surface area.
The combination of evaporation and condensation is used in the process of distillation to obtain pure water from a solution.
Saturated Solution: A solution in which no more of a substance (solute) can be dissolved at a given temperature.
📐Formulae
💡Examples
Problem 1:
How can we recover salt from a mixture of salt and water?
Solution:
By the process of evaporation. Heat the mixture in a beaker or a porcelain dish until all the water () turns into vapor, leaving the salt () crystals behind.
Explanation:
Salt is a non-volatile solute, meaning it does not turn into vapor easily, while water is volatile. Heating provides the necessary energy for .
Problem 2:
Explain the appearance of water droplets on the outer surface of a metal glass containing ice-cold water.
Solution:
This is due to the process of condensation.
Explanation:
The water vapor present in the air comes in contact with the cold surface of the metal glass. It loses heat energy and changes from the gaseous state () to the liquid state (), forming visible droplets.
Problem 3:
A mixture of sand and salt is dissolved in water. How can you separate all three components?
Solution:
- Filtration (to remove sand), 2. Evaporation (to turn water to vapor), 3. Condensation (to collect water).
Explanation:
First, use a filter paper to separate the insoluble sand. Then, heat the salt-water solution in a kettle. As steam () comes out of the spout, cool it using a metal plate with ice to condense it back into liquid water () in a separate beaker. The salt () remains in the kettle.