Chemistry - Year 6 - separation and solubility

Question 1

What are 5 methods of separation?

Answer 1

1. magnet
2. decanting
3. sieving
4. filtration
5. evaporation

Question 2

What is a mixture?

Answer 2

A MIXTURE is when two or more substances are mixed together but their atoms are NOT chemically bonded.

Mixtures can normally be separated easily by using physical methods rather than chemical reactions.

Question 3

What is a solution?

Answer 3

A SOLUTION is a mixture of a liquid in which at least one solid has been dissolved.

Question 4

What is a solvent?

Answer 4

A SOLVENT is the liquid part of a solution.

Question 5

What is a SOLUTE?

Answer 5

A SOLUTE is the solid dissolved within the solution.

Question 6

What does soluble mean?

Answer 6

Soluble is a substance which CAN be dissolved.

Question 7

What does insoluble mean?

Answer 7

Insoluble means a substance which CANNOT be dissolved.

Question 8

What does dissolved mean?

Answer 8

Dissolved means when a solid substance breaks apart into molecules which spread evenly throught a liquid.

Question 9

What is a saturated solution?

Answer 9

A saturated solution is a solution in which no more solid can be dissolved.

Question 10

What is a suspension?

Answer 10

A supension is when particles of solid are mixed with the liquid but are not dissolved.

Question 11

Air is a mixture of gases. Describe the mixture.

Answer 11

Air is a mixture of gases made from many which are not chemically bonded.

1. Nitrogen - 78%
2. Oxygen - 20%
3. Carbon Dioxide and water vapour - 1%
4. noble gases - 1%

Question 12

Describe how 3 different substances (salt, chalk and sand) behave when added to liquids.

Answer 12

• Salt dissolves in the water because it is soluble.
• The insoluble sand and chalk remain visible.

Question 13

Describe 3 ways to increase the rate that a certain mass of solute can be dissolved in a volume of water, e.g. 6g sugar into 50mls of water.

Answer 13

1. Increasing the temperature of the liquid - this puts more energy into the solution. (As the solution cools, some of the solid reappears.)
2. Stirring - this puts more energy into the solution.
3. Crushing the solid to increase the surface area before dissolving - this makes it easier for the sugar to “hide” in the water.

Question 14

Describe when you can separate a mixture using a magnet.

Give an example where this is used in practice.

Answer 14

Separation using a magnet:

In the special case where iron objects have become mixed up with non-magnetic materials, I can easily use a magnet to separate them.

Recycling companies use this method every day to separate out iron cans from heaps of rubbish.

Question 15

Describe decanting

Answer 15

Decanting

If the solid particles in my mixture are insoluble and sufficiently big and heavy, the mixture can be separated simply by pouring off the liquid (e.g. a bucket of water filled with stones).

This method is called decanting.

Question 16

Describe sieving as a method of separation.

Answer 16

Sieving

If my solid particles are insoluble but not heavy enough to stay in the container (as in the case of decanting) I could use a big sieve and pour the whole mixture through it. The water would pass through but the smaller stones would be caught on the mesh. This seiving method is also used in the kitchen when I drain pasta or vegtables after cooking. It will not work if the solid particles are smaller than the mesh.

Question 17

Describe filtration as a method of separation.

Answer 17

Filtration

Filtration is used to separate insoluble solids from mixtures. A practical example would be cafetieres or coffee filter machines.

In science we use the filter funnel and filter paper. Filter paper has tiny holes which let liquids and dissolved solids through (called the FILTRATE) but not insoluble solids (called the (RESIDUE).

Filtration will not work with solids that have dissolved in the solution.

Question 18

Describe evaporation as a method of separation.

Answer 18

Evaporation

If the liquid solvent is water then it can be removed by heating it to its boiling point. As the liquid evaporates into the air the insoluble solid particles are left behind.

Some countries produce purified salt and sell it around the world. They do this by pumping sea water onto fields. The hot sun evaporates the water leaving behind the salt, which is then harvested, purified and sold.

Question 19

How do I collect the liquid from a solution or separate two liquids? Describe and name the process.

Answer 19

Distillation.

Distillation is used to separate and collect a liquid solvent from a solution or to separate two or more liquids as long as they have different boiling points.

When a solution is boiled, the liquid evaporates. If the evaporated liquid is immediately collected and cooled, it condenses back into a liquid called the DISTILLATE. This combination of evaporation and condensation is the key to distillation.

Whiskey is made this way. Barley is mixed with water. Yeast is added which causes a chemical reaction that produces ethanol (alcohol). Ethanol has lower boiling point than water so when the mixture is distilled, the ethanol evaporates first. The ethanol condenses and is stored in barrels for several years, which helps to add flavour. It is then packaged and sold all around the world as whiskey.

Distilliation can even be used to separate gases. If air is cooled down enough, each gas will condense just below its boiling point and can be removed.

Question 20

Describe how and draw/label/name relevant apparatus to make distillation more efficient.

Answer 20

Simple distillation is not efficient enough. A better way of distilling is to use LIEBIG CONDENSER. The cetnral glass tube is cooled by a “cold water jacket”. The hot vapours are cooled more quickly, so more of the distillate is condensed and not lost to the atmosphere.

Where there are many parts of a mixture I can separate all of them at the same time by using fractional distillation. The different parts, or fractions, evaporate and condense at different temperatures.

Question 21

Describe why the water cycle is distillation in action.

Answer 21

• The sea water is warmed by the Sun and blown by the wind, which evaporates ONLY the water.
• This condenses to form clouds high up in the atmosphere which gather and release precipitation (rain, hail, sleet and snow).
• The water makes its way back to the sea in a variety of ways which involved dissolving solids and the filtration of water through ground rock.

Learn the diagram and be able to label it.

Question 22

Describe chromatography as a method of separation.

Answer 22

Chromatography is simply the separation of colours in a dye.

Chromatography will only work of the dyes are soluble. If the dyes are dissolved in a liquid solvent they are able to travel up or along the chromatography paper.

The MORE soluble dyes will travel FASTER and FURTHER.

The LESS soluble dyes will travel SLOWER and LESS FAR.

It is important to choose the correct solvent for our chromatopgraphy experiment. If our dyes are insolubel in water then they will not separate. A different solvent will have to be tried. Propanone (formerly called acetone) or ethanol can be used instead. Care must be taken and propanone and ethanol are highly flammable.