Separation of mixtures

Question 1

What is an element?

Answer 1

A pure substance that cannot be broken down into two or more simpler substances by chemical processes or electricity. Only one type of atom present, but can be monoatomic, diatomic, macromolecular, etc.

Question 2

What is a compound

Answer 2

A pure substance that contains two or more elements chemically combined. At least two types of atoms chemically bonded → categorised into ionic/covalent compounds. Cannot be separated by physical means.

Question 3

What is a mixture?

Answer 3

Two or more different types of substances not chemically bonded together (components retain original properties). No fixed ratio of components. Can be separated by physical means.

Question 4

Explain what filtration and decanting are used for

Answer 4

Used to separate a solid suspended in a liquid.

Question 5

Describe filtration.

Answer 5

Filter funnel to collect solid residue, while filtrate passes through into another beaker. Filter funnel to collect solid residue, while filtrate passes through into another beaker.

Question 6

Describe decanting.

Answer 6

Decanting is only used for larger particles. Top layer fucks off Otherwise, filtration is used (fine suspensions).
→ Residue can be further purified by washing it with distilled water, then drying between sheets of filter paper.

Question 7

What is evaporation to dryness and crystallisation used for?

Answer 7

Used to separate a solid dissolved in a liquid.

Question 8

Describe evaporation to dryness

Answer 8

→ Evaporating dish placed on a tripod stand and wire gauze, above a bunsen burner.
→ Solution is heated until no water is left and only a dry residue remains.

Question 9

Describe crystallisation

Answer 9

Solution is heated to saturation and allowed to cool until solid crystals form.

Question 10

What sort of salts are evap to dry/cryst not suitable for?

Answer 10

This method is not suitable for salts that can easily decompose.

Question 11

What is simple distillation used for?

Answer 11

to separate a solid dissolved in a liquid TO OBTAIN LIQUID.

Question 12

Describe simple distillation.

Answer 12

1. A distillation flask containing the solution to be distilled is placed over a Bunsen burner
2. A thermometer is placed in the flask but not into the substance
3. The thermometer is maintained at the temperature of the distillate’s boiling point
4. The distillate evaporates and travels into the Liebig condenser, condensing and being collected.

Question 13

What is the difference between crystallisation and simple distillation?

Answer 13

Crystallisation obtains substance with higher boiling point, while simple distillation obtains substance with lower boiling point.

Question 14

What is fractional distillation used for?

Answer 14

to separate two miscible (forms homogeneous mixture) liquids.

Question 15

Describe fractional distillation

Answer 15

→ Relatively similar setup as simple distillation, only with the addition of a fractionating column.
→ The thermometer must be maintained at the lower boiling point.
→ Fractionating column allows for the substance at a higher boiling point near to the distillate’s boiling point to condense within, as the column provides large surface area for it. This ensures that the distillate obtained is only the substance with the lower boiling point.
→ Fractional distillation separates mixtures with small differences in boiling points.

Question 16

Separating funnel: Used to separate two immiscible liquids.

Answer 16

In the seperatory funnel, the low density liquid is on top while the high density liquid is below.

Question 17

What properties are sought when determining how to separate two solid mixtures?

Answer 17

Can it be attracted by a magnet?
Is it soluble in water?
Is it able to sublime when heated?

Question 18

What is solution-filtration used for?

Answer 18

to separate a soluble and ins. solid

Question 19

When is sublimation used? Which substances are this applicable to?

Answer 19

Used when one solid is able to sublime and the other does not

Ammonium chloride
Iodine
Aluminium chloride
Naphthalene
Carbon dioxide

Question 20

Describe sublimation setup

Answer 20

An inverted funnel held by a retort stand is placed over an evaporating dish being heated.

Question 21

When is magnetism used? Which thing?

Answer 21

Used when one solid is attracted by a magnet, while the other is not
Iron, nickel, cobalt, steel, samarium-cobalt

Question 22

Why do we separate mixtures?

Answer 22

We separate mixtures for purification (obtain a clean sample of a component) and identification (analysing components of a mixture).

Question 23

Just say yes! You know paper chromatography!

Answer 23

PC is used to identify components of a mixture. The solvent must be able to dissolve all components of the sample mixture

Question 24

What is retardation factor?

Answer 24

Rf is a measure of the relative solubility of a pigment/substance in a particular solvent.
It is measured by Rf = distance moved by pigment / distance moved by solvent.

The more soluble the pigment, the higher the Rf value. It requires measurement of the solvent front, the furthest point travelled by solvent.

Question 25

Explain purity.

Answer 25

It is important that substances are pure, especially in medicine and food/beverages.
Impurities lower the melting point of a solid, and increase the boiling point of a temperature. It also causes the process of melting/boiling to take place over a range of temperatures.