S1 - Atoms (elements, compounds n mixtures)

Question 1

What is a atom?

Answer 1

The smallest particle of a chemical element that can exist - all substances are made up of atoms

Question 2

What is a molecule?

Answer 2

A group of atoms bonded together by covalent bonds (can be made up of one element or more than one element)

Question 3

What is an element?

Answer 3

Substances that consist of one type of atom that cannot be broken down any simpler by use of heat or electricity

Question 4

Give an example of an element

Answer 4

Copper (any element in the period table)

Question 5

What is a compound?

Answer 5

Substances made up of two or more different elements which are chemically joined together

Question 6

Give an example of a compound and how it is formed

Answer 6

Carbon dioxide - One carbon atom has boned with two oxygen atoms to form a molecule of carbon dioxide, with the formula CO2

Question 7

Why is it very difficult to separate two original elements after they have been chemically combined? Give an example

Answer 7

The properties of the compound are often totally different from the properties of the original element.

For example a mixture of iron and sulphur is heated and react togetehr to form iron sulphide. Iron sulphide isn’t like iron (not attracted to a magnet) nor like sulphur (not yellow)

Question 8

What is a mixture?

Answer 8

Molecules of elements and mixtures simply mixed together without chemical bonds

Question 9

Give two examples of a mixture

Answer 9

1) Air - is a mixture of gases mainly nitrogen, oxygen, carbon dioxide and argon
2) Crude oil - mixture of different lengths hydrocarbon molecules

Question 10

Can you separate mixtures easily and if so, with what methods?

Answer 10

Yes - there are no chemical bonds between the different parts of a mixture so can be separated by the following physical methods;

• Distillation
• Fractional
• Filtration
• Crystallisation
• Paper chromatography

Question 11

What is a solvent?

Answer 11

The liquid in which a solute dissolves

Question 12

What is a solute?

Answer 12

The substance that dissolves in a liquid to form a solution

Question 13

What does soluble mean?

Answer 13

A substance that can dissolve

Question 14

What does insoluble mean?

Answer 14

A substance that cannot dissolve

Question 15

What is filtration used to separate?

Answer 15

Insoluble solids from a liquid (and purification)

Question 16

What is crystallisation used for?

Answer 16

Separating soluble solids from a solution

Question 17

What is the method for crystallising a product?

Answer 17

• Pour solution in evaporating dish
• Slowly heat until crystals start to form then stop *solvent evaporates solution making it more concentrated
• Remove dish from heat and put in warm place *rest of solvent will evaporate
• Dry the product (either in a drying oven or desiccator)

Question 18

What does a desiccator contain?

Answer 18

Chemicals that remove water from the surroundings

Question 19

What can you separate using both filtration and crystallisation!

Answer 19

Rock salt

Question 20

What is rock salt and what is it about their physical properties that make them easy to separate?

Answer 20

Rock salt is a mixture of salt and sand. Salt and sand are both compounds but salt dissolves in water and sand doesn’t

Question 21

Give the four steps for separating rock salt

Answer 21

1) Grinding - grind rock and salt with a pestle and mortar
2) Dissolve - dissolve in beaker and stir
3) Filtering - filter through filter paper in a funnel
4) Crystallisation - evaporate in a evaporating dish

Question 22

Why does sand collect in the filter paper?

Answer 22

It is insoluble (doesn’t dissolve), so stays as big grains. These wont fit through the tiny holes in the filter paper

Question 23

Why does salt go through the filter paper?

Answer 23

It is soluble and dissolved in the solution - when water is evaporated from it, the salt forms a crystal in the evaporating dish

Question 24

What is chromatography in particular paper chromatography?

Answer 24

Another method for separating out mixtures - paper chromatography separates out dyes

Question 25

Go through the method of chromatography

Answer 25

1) Draw a line near the bottom of the filer paper (in pencil) 2) Add spots of different dyes to the line in regular intervals 3) Attach a lollipop stick to the top of the sheet and dip a tiny bit of the paper into beaker of solvent 4) The solvent seeps up the paper carrying the dyes with it 5) Each dyes moves up at different rates and forms spots 6) The end result is called chromatogram.

Question 26

Why should you draw the line with pencil not pen?

Answer 26

Pencil marks are insoluble and wont react with the solvent

Question 27

When you dip the paper in the solvent why should you make sure that the dyes aren't touching the solvent?

Answer 27

So they don't dissolve in it

Question 28

Why does chromatography seperate mixtures?

Answer 28

It works because different dyes move up the paper at different rates. Some stick to the paper and others will dissolve more readily in the solvent and travel more.

Question 29

The distance the dyes travel up the paper depend on what?

Answer 29

The solvent and the paper used

Question 30

How can chromatography help identify dyes?

Answer 30

You can work out dyes that are present in an unknown substance by making chromatograms of the unknown substance and for some reference materials (dyes you think are in it) You then compare the chromatograms - spots on the chromatograms roe the unknown that match the spots on the chromatograms of the reference materials means the dyes are the same

Question 31

What are the two types of distillation called?

Answer 31

Simple and fractional

Question 33

Describe what happens in simple distillation

Answer 33

1) The solution is heated - the part with the lowest bp evaporates 2) The vapour is then cooled, condenses (turns back to a liquid) and collected 3) The rest of the solution is left behind in the flask

Question 34

Give an example of a solution you could seperate in simple distillation

Answer 34

Pure water from seawater - you'll end up with salt left in the flask

Question 35

What is the problem with simple distillation which makes fractional distillation better?

Answer 35

You can only separate things with very different bp in simple distillation

Question 36

Describe what happens in fractional distillation

Answer 36

1) You put your mixture in a flask then stick a fractionating column on top - heat it 2) The liquid with the lowest bp evaporates first (when the temp on the thermometer matches the bp it reaches the top of the column) 3) Liquids with the highest bp might also evaporate (only bet part of the way before condensing because column is cooler 4) When the first liquid has collected you raises the temperature until the next one reaches the top

Question 37

What is simple distillation used to seperate out?

Answer 37

Solutions - liquids