Tag: crystals and crystallisation

Questions Related to crystals and crystallisation

To crystallize copper sulphate, it is dissolved in water and a small quantity of ................. is also added.

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. concentrated nitric acid

  2. dilute hydrochloric acid

  3. dilute sulphuric acid

  4. dilute nitric acid

Show answer
Correct Option: C
Explanation:

To crystallise copper sulphate, water is dissolved and a small quantity of dilute sulphuric acid is added to prevent the hydrolysis of copper sulphte. The impurities left behind in the solution are removed by filtration.

During crystallization of copper sulphate, heating is stopped when :

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. solution becomes saturated

  2. solution reaches boiling point

  3. solution is reduced to half of its quantity

  4. the solution is not heated at all

Show answer
Correct Option: A
Explanation:

Crystallization process begins with dissolving the impure copper sulphate sample in water and then heating it. It is heated to saturation rather than dryness and once it is saturated the heating is stopped and the solution is allowed to cool.

Copper sulphate crystals are of which color after purification?

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. White

  2. Black

  3. Blue

  4. Yellow

Show answer
Correct Option: C
Explanation:

To crystallise copper sulphate, it is dissolved in water and a small quantity of dilute sulphuric acid is added to prevent the hydrolysis of copper sulphte. The impurities left behind in the solution are removed by filtration. The filtrate is concentrated to the crystallisation point and then cooled. On cooling, transparent blue crystals of copper sulphate separate.

When are the crystals of copper sulphate obtained?

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. when hot acidic copper sulphate solution is cooled gradually.

  2. when cold acidic copper sulphate solution is heated gradually.

  3. when hot acidic copper sulphate solution is cooled suddenly.

  4. when cold acidic copper sulphate solution is heated suddenly

Show answer
Correct Option: A
Explanation:

When hot acidic $ copper : sulphate$ solution is cooled gradually, the crystals of  $ copper : sulphate$ are obtained.

Soda water can be separated by lowering the pressure.

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Soda water can be separated by lowering the pressure. When pressure is lowered, the solubility of soda ( or any gas) in water decreases. Hence, soda will escape out.

Which method is used to separate diastereomers?

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. Distillation

  2. Fractional Crystallisation

  3. Sublimation

  4. Evaporation

Show answer
Correct Option: B
Explanation:

Diastereomers have different physical properties. You can separate them by ordinary separation techniques such as fractional crystallization. 


Then you treat the separated diastereomers with appropriate reagents to regenerate the original enantiomers.

Option B is correct.

The method by which common salt is obtained from concentrated seawater is called:

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. Crystallisation

  2. Catalyst

  3. Hydrolysis

  4. Evaporation

Show answer
Correct Option: A
Explanation:

The method by which common salt is obtained from concentrated seawater is called crystallisation.


Crystallisation is a technique used to separate a solid from a solution. The solid is more soluble at a higher temperature and less soluble at a lower temperature.

Hence, option A is correct.

The crystals that are obtained after crystallization are:

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. more than 90% pure

  2. between 40% and 80% pure

  3. between 10% to 40% pure

  4. 10% pure

Show answer
Correct Option: A
Explanation:

Crystal is the pureset form of a compound, the method of forming crystals is known as crystallization, crystals are more than 90% pure and its purity can be increased upto 99.9% by recrystallization technique.  

Why crystallisation is used for obtaining pure copper sulphate from an impure sample rather than simple evaporation?

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. Some impurities may remain dissolved in the solution even after filtration. On evaporation, these may contaminate the solid

  2. Because crystallisation is comparatively easier than evaporation

  3. Because crystallisation is comparatively faster

  4. All of the above

Show answer
Correct Option: A
Explanation:

Crystallisation technique is better than simple evaporation technique as some solids decompose and some impurities may remain dissolved in the solution even after filtration. On evaporation, these contaminate the solid.

Crystals of pure copper sulphate are separated from the solution by :

chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

  1. condenstaion

  2. distillation

  3. solidification

  4. filtration

Show answer
Correct Option: D
Explanation:

Pure copper sulphate can be obtained from an impure sample by re-crystallization. The impure sample is dissolved in water, heated and then cooled which then later forms crystals. These copper sulphate crystals are then separated by filtration and drying.