S1 - Atoms (elements, compounds n mixtures)
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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