S1 - Atoms (elements, compounds n mixtures) Flashcards
What is a atom?
The smallest particle of a chemical element that can exist - all substances are made up of atoms
What is a molecule?
A group of atoms bonded together by covalent bonds (can be made up of one element or more than one element)
What is an element?
Substances that consist of one type of atom that cannot be broken down any simpler by use of heat or electricity
Give an example of an element
Copper (any element in the period table)
What is a compound?
Substances made up of two or more different elements which are chemically joined together
Give an example of a compound and how it is formed
Carbon dioxide - One carbon atom has boned with two oxygen atoms to form a molecule of carbon dioxide, with the formula CO2
Why is it very difficult to separate two original elements after they have been chemically combined? Give an example
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)
What is a mixture?
Molecules of elements and mixtures simply mixed together without chemical bonds
Give two examples of a mixture
1) Air - is a mixture of gases mainly nitrogen, oxygen, carbon dioxide and argon
2) Crude oil - mixture of different lengths hydrocarbon molecules
Can you separate mixtures easily and if so, with what methods?
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
What is a solvent?
The liquid in which a solute dissolves
What is a solute?
The substance that dissolves in a liquid to form a solution
What does soluble mean?
A substance that can dissolve
What does insoluble mean?
A substance that cannot dissolve
What is filtration used to separate?
Insoluble solids from a liquid (and purification)
What is crystallisation used for?
Separating soluble solids from a solution
What is the method for crystallising a product?
- 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)
What does a desiccator contain?
Chemicals that remove water from the surroundings
What can you separate using both filtration and crystallisation!
Rock salt
What is rock salt and what is it about their physical properties that make them easy to separate?
Rock salt is a mixture of salt and sand. Salt and sand are both compounds but salt dissolves in water and sand doesn’t
Give the four steps for separating rock salt
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
Why does sand collect in the filter paper?
It is insoluble (doesn’t dissolve), so stays as big grains. These wont fit through the tiny holes in the filter paper
Why does salt go through the filter paper?
It is soluble and dissolved in the solution - when water is evaporated from it, the salt forms a crystal in the evaporating dish
What is chromatography in particular paper chromatography?
Another method for separating out mixtures - paper chromatography separates out dyes
Go through the method of chromatography
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.
Why should you draw the line with pencil not pen?
Pencil marks are insoluble and wont react with the solvent
When you dip the paper in the solvent why should you make sure that the dyes aren’t touching the solvent?
So they don’t dissolve in it
Why does chromatography seperate mixtures?
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.
The distance the dyes travel up the paper depend on what?
The solvent and the paper used
How can chromatography help identify dyes?
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
What are the two types of distillation called?
Simple and fractional
Describe what happens in simple distillation
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
Give an example of a solution you could seperate in simple distillation
Pure water from seawater - you’ll end up with salt left in the flask
What is the problem with simple distillation which makes fractional distillation better?
You can only separate things with very different bp in simple distillation
Describe what happens in fractional distillation
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
What is simple distillation used to seperate out?
Solutions - liquids
