1b Elements, compounds and mixtures

Question 1

What is an element?

Answer 1

A substance that cannot be broken down into simpler substances by chemical methods

Question 2

What is an atom?

Answer 2

The smallest part of an element that can exist on its own

Question 3

What is a molecule?

Answer 3

A combination of atoms

Question 4

What is a compound?

Answer 4

A substance containing two or more elements joined together

Question 5

What is a mixture?

Answer 5

Different substances but not chemically joined in any way

Question 6

What is chromatography?

Answer 6

Separation technique used to separate the colours in dyes and inks that relies on the affinity of components of a mixture to a mobile phase and a stationary phase

The colours with a higher solubility will spread further than others - they will have a higher Rf value for that solvent

If the dye doesn’t move at all that means it insoluble in that solvent

Question 7

What is the mobile phase?

Answer 7

This is the phase that is a carrier for the components as they travel through the stationary phase

Solvent + (water, ethanol)

Question 8

What is the stationery phase?

Answer 8

This is the phase that is stationery

Paper

Question 9

How to calculate Rf values?

Answer 9

• Distance travelled by component
• Distance travelled by mobile phase
• Specific to each plate
• Comparable
• Each component on the plate has unique Rf value
  Rf = distance travelled by dye/distance travelled by solvent
  Rf = 2.1/2.8 = 0.75

Question 10

What is a mixture?

Answer 10

Different substances but not chemically joined in any way

Question 11

What is a solution?

Answer 11

The mixture formed when a solute is dissolved in a solvent

Question 12

What is a solvent?

Answer 12

The thing that does the dissolving
eg. water and ethanol

Question 13

What is a solute?

Answer 13

The thing that is dissolved
eg. salt

Question 14

What does soluble mean?

Answer 14

Is a solid that can be dissolved (disappears) in a solvent eg. sugar

Question 15

What does insoluble mean?

Answer 15

A soli which is not soluble
eg. sand

Question 16

What is the filtrate?

Answer 16

Is the liquid part of a mixture that is filtered

Question 17

What is residue?

Answer 17

Insoluble solid that is left in filter paper

Question 18

What is distillate?

Answer 18

The liquid that evaporates and condenses as a result of distillation

Question 19

What is crystallisation?

Answer 19

Crystals left when the saturated solution is left to evaporate slowly

Question 20

What is distillation?

Answer 20

A method used to separate a liquid from the solids dissolved in it
Distillation = Evaporation + Condensation

Question 21

What is simple distillation?

Answer 21

Simple distillation is used to separate the solvent and solute in a solution in order to collect the pure solvent.
The solution is put in a flask with anti bumping granules to allow smooth boiling.
The heat from the Bunsen burner evaporates the solvent. The vapour then rises and enters the Liebig condenser.
The condenser cools the vapour to turn it back into a liquid. This pure liquid is called the distillate

Question 22

What is fractional distillation?

Answer 22

Fractional distillation separates mixtures of two or more miscible liquids (liquids that mix). For example, ethanol and water.

The mixture is heated in a flask with anti-bumping granule. Both liquids evaporate and their vapour enters the fractionating column. The column has a temperature gradient which is hotter near the bottom and cooler near the top.

Because ethanol has a lower boiling point it quickly rises up the column, enters the condenser and condenses back to a liquid. Water has a higher boiling point, so it condenses near the bottom of the fractionating column and remains in the flask.