Chemistry unit 1.2 Mixtures

Question 1

What is a mixture?

Answer 1

Two or more elements or compounds not chemically combined together.

Question 2

What happens to the chemical properties of each substance?

Answer 2

They are unchanged

Question 3

What is the law of conservation of mass

Answer 3

The total mass of products formed in a reaction is equal to the total mass of the reactants.

Question 4

How are mixtures seperated?

Answer 4

physical processes that do not involve chemical reactions, no new substances are made.

Question 5

What are the methods used to seperate mixtures?

Answer 5

filtration, crystallisation, simple distillation, fractional distillation and chromatography

Question 6

What is filtration used for? Give an example

Answer 6

• Used to separate an insoluable(cant dissolve) solid from liquid ( e.g., sand from a mixture of salt and water)

Question 7

Method of filtration

Answer 7

• A piece of filter paper is placed in a filter funnel above a beaker
• A mixture of insoluble solid and liquid is poured into the filter funnel
• The filter paper will only allow small liquid particles to pass through as filtrate
• Solid particles are too large to pass through the filter paper so will stay behind as a residue

Question 8

What is crystallisation used for? Give an example

Answer 8

Used to separate a soluble solid from a solution

Question 9

Method of crystallisation

Answer 9

-Pour solution into evaporating dish, gently heat.
- some solvent will evaporate when you see crystals start to form (point of crystallisation) remove dish from heat and leave to cool.
-The salt would start to form as it becomes insoluble in the cold.
- filter out crytals from solution and leave in warm place to dry.

Question 10

What is simple distillation used for? Give an example

Answer 10

Seperating out a liquid from a solution. E.g pure (water from a solution of salt water)

Question 11

Method of simple distillation

Answer 11

• The solution is heated and the part of solution that has lowest boiling point evaporates first.
• produces a vapor which rises through the neck of the round-bottomed flask (e.g. for saltwater, this would be water boiling at 100 oC)
  The vapor passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
  After all the liquid is evaporated from the solution, only the solid solute will be left behind.

Question 12

What is fractional distillation used for? Give an example

Answer 12

Used to seperate a mixture of liquids. E.g crude oil

Question 13

Method of fractional distillation

Answer 13

• put mixture in a flash eith fractionating column on top.
• Heat it, different liquids have different boiling points so will evaporate at different temperatures.
• the liquid with the lowst boiling point evaporates first, when temp on thermometer matches boiling point of this liquids it reaches top of column.
  -liquids with higher boiling points might also start to evaporate, colum cooler at top so condense and come back into flask.
  -when first liquid collected, raise temp until next reaches the top.

Question 14

What is chromotography used for? Give an example

Answer 14

Seperate substances in a liquid, E.g dyes in ink

Question 15

Method of chromotography

Answer 15

• A pencil line is drawn on chromatography paper and spot of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples.
• The paper is then lowered into beaker with solvent, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
• The solvent travels up the paper, taking some of the coloured substances with it
• Different substances have different solubilities so will travel at different rates, causing the substances to spread apart
• Those substances with higher solubility will travel further than the others
  This will show the different components of the ink / dye