Chapter 3: Separation and Purification

Question 1

Separating Insoluble solid from a liquid.

Answer 1

Filtration

Question 2

Why do we use filtration?

Answer 2

• Filter paper acts as a sieve
• Filtrate can pass through the pores of filter paper
• Residue remains on the filter paper

Question 3

Separating Soluble solids from liquid. (2 mtds)

Answer 3

Evaporation to dryness or Crystallisation

Question 4

The solid obtained through Evaporation to dryness is pure. True or false?

Answer 4

• False
• Solid obtained is not always pure
• InsoLuble impurities will be left tgt with solid after all the water has been boiled off
• Hence, it is false

Question 5

When do we use Crystallisation?

Answer 5

• When separating soluble solids from liquid
• Subst decompose when heated strongly
• To obtain a pure solid sample frm solution

Question 6

State the 4 steps during Crystallisation.

Answer 6

1. Solution is heated until most of the water hasboiled off
2. Hot saturated solution is obtained
3. Hot saturated solution= set aside to cool down = to room temperature
4. After cooling down= dissolved solid formed as PURE CRYSTAL

Question 7

State the 2 steps after pure crystal solid is formed during crystallisation.

Answer 7

1. Wash crystals with a little cold distilled water
2. To remove impurities
3. Pat crystals dry between a few sheets of filter paper

Question 8

State the 2 methods of separating 2 liquids.

Answer 8

Simple distillation and fractional distillation

Question 9

What is the aim of simple distillation?

Answer 9

-Separate a pure solvent (liquid) from the solution and -obtain PURE subst in liquid from its solution

Question 10

What happens during fractional distillation?

Answer 10

1. Liquid with lowest b.p distil over first

2. Vapours of liquid with higher b.p =condense along the fractionating column = fall back into the round-bottomed flask

Question 11

Why is there many glass beads in the fractionating columns ?

Answer 11

provide larger surface area= for vapour to condense on

Question 12

Method: Separating 2 or more components that dissolve in the same solvent

Answer 12

Paper chromatogram

Question 13

What is the aim of paper chromatogram?

Answer 13

determine the purity of a subst/sample

Question 14

A substance melts faster over a range of tempt and boils slower over a range of tempts as compared to other substance. Why?

Answer 14

• Impure substance

- Impurities lowers the m.p of a subst and increases the b.p of a subst

Question 15

Why do we use simple distillation?

Answer 15

-Obtain a solvent from a mixture of a solvent and a solution.