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SS1: CHEMISTRY - 1ST TERM

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  1. Introduction to Chemistry and Laboratory Apparatus | Week 1
    5Topics
    |
    1 Quiz
  2. Nature of Matter | Week 2
    3Topics
    |
    1 Quiz
  3. Separation Techniques I | Week 3
    1Topic
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    1 Quiz
  4. Separation Techniques II | Week 4
    5Topics
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    1 Quiz
  5. Particulate Nature of Matter I | Week 5
    5Topics
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    1 Quiz
  6. Particulate Nature of Matter II | Week 6
    9Topics
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    1 Quiz
  7. Symbols, Formulae & Oxidation Number | Week 7
    7Topics
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    1 Quiz
  8. Laws of Chemical Combination | Week 8
    4Topics
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    1 Quiz
  9. Chemical Equation & Chemical Combination (Chemical Bonding) I | Week 9
    4Topics
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    1 Quiz
  10. Chemical Combination (Chemical Bonding) II | Week 10
    4Topics
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    1 Quiz
  11. Chemical Combination (Chemical Bonding) III & Shapes of Covalent Molecules | Week 11
    3Topics
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    1 Quiz
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Chromatography is a method used to separate components of a complex mixture in a solution. There are many types of chromatography.

1. Paper chromatography.

2. Column chromatography.

3. Thin-layer chromatography.

4. Gas chromatography.

Paper Chromatography

This can be used to separate components of complexes like leaf extract or black ink. Filter paper is used as the absorbent medium and alcohol is used as a solvent. A drop of the complex (ink or leaf extract) is blotted at a predetermined distance from the edge of the paper. The paper is hung inside a dish containing alcohol (ethanol). As the solvent carries the extract along the paper, the components separate out into different colours. This is because the rates of movement of the different components inside the solvents are not the same.

Chromatography

In chromatography, there are two phases. A stationary phase (filter paper) on which the solutes are adsorbed. A mobile phase (alcohol) which dissolves the solute and carries them.

Column Chromatography

In column chromatography, a glass tube is used as the column while an adsorbent such as powdered Alumina (Aluminium oxide), magnesium, or calcium trioxocarbonate (IV) is used as the Stationary Phase. A suitable solvent is used as the mobile phase.

The complex mixture in solution is poured down the column (of adsorbent in glass). Then the pure solvent is poured into the column. The components are separated due to their different rates of flow as well as their different rates of adsorption to the column.

column Chromatography

Uses/Application of Chromatography

1. In analysing complex mixtures.

2. Identifying the components of petroleum fractions.

3. Monitor the progress of a chemical reaction.

4. Analyze blood and urine samples.

Theory Questions

1. What method would you use to separate the following?

(a) Mixture of two solids which have widely different solubilities in water

(b) A mixture of two liquids which have widely different boiling points.

(c) A pure solid from a concentrated solution of its salt

(d) The component colours of leaf

(e) An aqueous solution of Lead (ii) and copper (ii) ions

View Answer

2. (a) What is Sublimation? 

(b) Name two substances that can undergo Sublimation

View Answer

3 (a) Describe how you will separate the components of black ink. Name the process. 

(b)Name two other complex mixtures you can separate by the above-named process.

View Answer

4. A five-year-old boy was sent to buy salt by his mother, on his way back the salt fell and mixed with sand. As a chemistry student describe the steps you would follow to help the boy get back the salt without buying another one for him.

View Answer

5 (a) State one difference between Crystallization and Evaporation to dryness    

(b) List two methods that can be used to separate a mixture of Iodine crystal and Iron filings 

(c) State one industrial application of (i) Crystallization (ii) Chromatography

View Answer

Theory Question 1

What method would you use to separate the following?

(a) Mixture of two solids which have widely different solubilities in water

AnswerCrystallization

(b) A mixture of two liquids which have widely different boiling points

Answer  – Simple distillation

(c) A pure solid from a concentrated solution of its salt

Answer Crystallization

(d) The component colours of leaf

Answer  – Chromatography

(e) An aqueous solution of Lead (II) and copper (II) ions

Answer  – Precipitation

Theory Question 2

(a) What is Sublimation? 

Answer Sublimation is a term that describes the change in a solid substance directly to gas or gas when cooled, directly to solid without passing through the intermediate liquid; when heat is applied.

(b) Name two substances that can undergo Sublimation

Answer –

(i) iodine

(ii) camphor

Theory Question 3

(a) Describe how you will separate the components of black ink. Name the process. 

Answer:

The method used to separate the components of black ink is paper chromatography.

In this process, the filter paper is used as the adsorbent medium and alcohol, as a solvent. A drop of the ink is blotted at a predetermined distance from the edge of the paper. The paper is hung inside a dish containing alcohol. As the solvent carries the extract along the paper, the components separate out into different colours. This is as a result of the rates of movement of the various components i.e. the rates of movement of these components are not the same.

(b)Name two other complex mixtures you can separate by the above-named process.

Answer 

i. Leaf extracts

ii. dyes

Theory Question 4

A five-year-old boy was sent to buy salt by his mother, on his way back the salt fell and mixed with sand. As a chemistry student describe the steps you would follow to help the boy get back the salt without buying another one for him.

Answer:

Dissolve the mixture (sand and salt) at a high temperature. Allow the solution to cool (in order to allow the sand to settle out).

Procedure 2 – Heat the salt solution to evaporate a portion of the solvent in order to obtain a saturated solution. On cooling, the sand will appear. Filter the sand and dry the salt in a filter paper.

Theory Question 5

5 (a) State one difference between Crystallization and Evaporation to dryness

Answer:    

Evaporation is used to recover a soluble solute from a solution.

While

Crystallization is a process of formation of solid crystals from a precipitating solution

(b) List two methods that can be used to separate a mixture of Iodine crystal and Iron filings

Answer: 

(i) Magnetization (ii) Sublimation

(c) State one industrial application of (i) Crystallization (ii) Chromatography

Answer:

(i) Crystallization – It is widely used in the pharmaceutical industries as a purification and separation process

(ii) Chromatography – It is applicable in flavour studies and also in detecting food spoilage

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