Elements, compounds and mixture

Question 1

Element

Answer 1

A substance made up of the same atoms
Examples: oxygen, carbon, hydrogen

Question 2

Compounds

Answer 2

A pure substance made up of two or more elements, which are chemically bonded together.
Cannot be separated by physical methods of separation.
Examples: calcium carbonate, copper (III) sulphate

Question 3

Mixtures

Answer 3

A combination of two or more substances (elements and/or compounds) that are physically mixed together, and are not chemically combined
Can be separated by physical methods of separation.
Examples: salt and water, air

Question 4

Physical methods of separation

Answer 4

Evaporation, distillation, filtration…

Question 5

Pure Substance

Answer 5

Consist of a single element or compound which contains no other substances

Question 6

Pure Substance boiling/melting points

Answer 6

Has fixed melting and boiling point as they consist of only one substance so all molecules will have the same melting and boiling points.

Question 7

Mixture boiling/melting points

Answer 7

Has a range of melting and boiling point as they consist of different substances that melt or boil at different temperatures.

Question 8

Experiment: Simple Distillation

Answer 8

1. Solution is heated and water vapours will rise and evaporate
2. Water vapours will pass through the condenser, where it cools and condenses, turning into a liquid that will be collected in a beaker
3. After all water is evaporated from solution, the solute will be left behind

Question 9

Experiment: Fractional Distillation

Answer 9

1. Solution is heated at temperature of substance with lowest boiling point
2. Substance will rise and evaporate, vapours will pass through condenser –> where it cools and condenses, turning into liquid that will collected in beaker
3. All of this substance is evaporated and collected, leaving behind a mixture or a substance

Question 10

Experiment: Filtration

Answer 10

1. Filter paper is placed in a filter funnel above another beaker
2. Mixture of insoluble solid and liquid is poured into the filter funnel
3. Filter paper will only allow small liquid particles to pass through as the filtrate
4. Solid particles too large to pass through filter paper so will stay behind as a residue

Question 11

Crystallisation

Answer 11

1. Solution is heated, allowing the solvent to evaporate to leave a saturated solution
2. Saturated solution is allowed to cool and solids will come out of the solution and crystals will grow
3. Crystals are collected and allowed to dry

Question 12

Chromatography

Answer 12

1. Pencil line is drawn on chromatography paper and spots of ink/dye is placed on it
2. Paper is lowered into a bucket of solvent, allowing the solvent to travel up the paper, taking some of the coloured substances with it
3. Different substances will have different solubilities so will travel at different rates, causing the substances to spread apart
4. The paper will show the different components of the ink

Question 13

how a chromatogram provides information about the composition of a mixture

Answer 13

Shows the composition of a mixture as the different coloured substances will spread apart as they will have different solubilities so will travel at different rates.

Question 14

Pure substance in chromatography

Answer 14

A pure substance will only produce one spot on the chromatogram during paper chromatography.

Question 15

Calculate the Rf

Answer 15

Rf = distance travelled by substance ÷ distance travelled by solvent
- The Rf value will always lie between 0 and 1; the closer it is to 1, the more soluble is that component in the solvent

Question 16

Practical: Investigate paper chromatography using inks/food colorings:

Answer 16

1. Draw line on chromatography paper and place spots of ink/dye on it.
2. Lower paper into a bucket of solvent, allowing the solvent to travel up the paper, taking some of the coloured substances with it.
3. Allow chromatography to occur until the solvent reaches the top of the paper.
4. As the solvent travels up the paper, the substances to spread apart. This is because different substances will have different solubility’s, so they will travel at different rates
5. This will show the different components of the ink