SC1 & SC2: States of Matter / Purifying Substances

Question 1

SC2a Mixtures

Describe the differences between a Pure Substance & a Mixture.

Answer 1

A) Pure Substance
1. Is only made up of one type of element or compound

2. Melts/Boils at consistent temperatures due to it having the same composition throughout.

3. Cannot be separated through physical means.

B) Mixtures
1. Made up of more than 1 type of element or compound.

2. Melts/Boils at a range of temperatures due to it being a mixture of different substances that melt/boil at different temps.

3. Can be separated through physical means.

Question 2

SC2b Filtration and Crystallisation

A) What is Crystallisation?
B) Describe a method to obtain Salt Crystals from Sea Water.

Answer 2

A) It is a method to seperate solutes from a solution by evaporating the solvent to leave the** solute** behind.

B) Method

1. First set up a filter funnel lined with filter paper that is used to remove the large insoluble objects in the water.
- This forms the filtrate

2. A Bunsen Burner is then used to evaporate that filtrate, leaving behind crystals that require time to cool.

Possible Risk;
1. Burning on the Bunsen Burner - Wear gloves and don’t stay to close.
2. Spitting hot crystals - Wear eye protection.

Question 3

SC2c Paper Chromatography

A) What is the Rf value?
B) What are the uses of Paper Chromatography?

Answer 3

A) Rf value refers to the distance the compound has risen divided by the distance the solvent has risen.

B) Some uses are;
- To distinguish between pure and impure substances.
- Identify substances by comparing the patterns on chromatgram with known substances.
- Identify substances with their Rf value.

Question 4

SC2d Distillation

A) Describe what Simple Distillation is.
B) Describe the uses of Fractional Distillation.

Answer 4

A) Simple Distillation is method to obtain water from mineral water, as the solids evaporate at a much higher temperature than water.
- This is done through; 1. Heating in a conical flask, 2. Let the air vapour travel through the condensation tube.
- This method isn’t very effective as a lot of the vapour is lost.

B) Uses include;
- To separate the different products in crude oil
- To make make alcholic drinks such as wisky and vodka
- To separate out the gases in the air, after the air has been cooled and turned into liquid at -200C

Question 5

SC2e Drinking Water

Describe the different needs for water purification.

Answer 5

1. Sea water purification
- Water can be separated from salts using simple distillation.
- Done by; Heating the Sea water so that water vapour leaves it quickly before cooling it down again.

2. Water for Chemical Analysis
- Water used for chemical analysis should not contain any dissolved salts, otherwise incorrect results may appear.
- Also the machines used for analysis may detect the salts, resulting in an error.

3. Drinking Water
- Fresh water contains many harmful things, like;
- Objects such as leave and twigs
- Small insoluble objects like grit
- Soluble objects like pesticide and fertilisers
- Microrganisms