Tag: crystals and crystallisation

Questions Related to crystals and crystallisation

Why is dilute sulphuric acid added during crystallization of copper sulphate?

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

  1. Prevent hydrolysis of copper sulphate

  2. Prevent crystallization of copper sulphate

  3. Enhance formation of large crystals

  4. All of the above

Show answer
Correct Option: A
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.

Which of the following can be separated by crystallization?

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

  1. Copper sulphate

  2. Benzoic acid

  3. Potash alum

  4. All of above

Show answer
Correct Option: D
Explanation:

Crystallization is a method of purification by the formation of crystals. 


The above samples can be separated by crystallization by heating the solution and then cooling them to form crystals.

Hence the correct option is D.

Technique utilized to separate a mixture of dissolved solids by evaporation according to individual solubilities.

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

  1. Distillation

  2. Chromatography

  3. Fractional crystallization

  4. Filtration

  5. Titration

Show answer
Correct Option: C
Explanation:

Technique utilized to separate a mixture of dissolved solids by evaporation according to individual solubilities is fractional crystallization. Two solutes have different solubilities in the same solvent at the same temperature. Fractional crystallization is step-wise crystallization. First, less soluble solute is crystallized out. Later, more soluble solute is crystallized out.

Usually crystals are dried with help of ________.

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

  1. dryer

  2. autoclave

  3. filter paper

  4. fan

Show answer
Correct Option: C
Explanation:

Usually crystals are dried with help of filter paper.
The moisture present in the crystals is absorbed by filter paper.

Why does crystallisation seperate mixtures?

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

  1. Because the components do not chemically combine

  2. Because the components have different boiling point

  3. Because the components have different solubilities at high and low temperatures

  4. None of these

Show answer
Correct Option: C
Explanation:

The crystallization can separate mixtures because the components have different solubilities at high and low temperatures. The solute to be crystallized is more soluble in hot solution than in cold solution.

Crystals can be grown by _________.

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

  1. cooling a saturated solution

  2. heating a saturated solution

  3. stirring a saturated solution

  4. planting in a well watered fertile soil

Show answer
Correct Option: A
Explanation:

Cooling a saturated solution. (Heating is stopped at the point when a hot saturated solution is formed. If the resulting solution is allowed to cool to room temperature, the dissolved solid will precipitate out as pure crystals.)

How would you know if a solution is saturated?

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

  1. When a sample is taken out and cooled, it forms small crystals rapidly

  2. When the sample starts to evaporate

  3. When more solid is added, they continue to dissolve in the solution

  4. When solution changes colour

Show answer
Correct Option: A
Explanation:

When a sample is taken out and cooled, it forms small crystals rapidly.(At a given temperature, a solution can only hold a certain amount of solute.A saturated solution is one that contains the maximum amount of solute at a given temperature.)

The most suitable method of separation of $1$ mixture of ortho and para-nitrophenols is:

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

  1. crystallisation

  2. steam distillation

  3. sublimation

  4. chromatography

Show answer
Correct Option: B
Explanation:

The most suitable method of separation of 1:1 mixture of ortho and para-nitrophenols is steam distillation because they have a great difference in their boiling points. Hence, option B is correct.

What would you observe when a saturated solution of potassium chloride prepared at $60^0 C$ is allowed to cool to room temperature?

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

  1. Crystallization happens

  2. Evaporation happens

  3. Sublimation happens

  4. Condensation happens

Show answer
Correct Option: A
Explanation:

Here crystallization happens and solid potassium chloride will separate out. (Crystallization is a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs)

Arrange the following steps in crystallisation of copper sulphate.
A. Dissolve it in minimum amount of water.
B. Take some (approximately 5 g) impure sample of copper sulphate in a china dish.
C. Cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day.
D. Evaporate water from the copper sulphate solution so as to get a saturated solution.
E. Filter the impurities out.

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

  1. A, C, B, D, E

  2. B, D, A, C, E

  3. B, A, D, E, C

  4. B, A, E, D, C

Show answer
Correct Option: C
Explanation:

The correct order of steps in crystallisation of copper sulphate is B, A, D, E, C.
B. Take some (approximately 5 g) impure sample of copper sulphate in a china dish.
A. Dissolve it in minimum amount of water.
D. Evaporate water from the copper sulphate solution so as to get a saturated solution.
E. Filter the impurities out.
C. Cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day.