1 Elements, Compounds and Mixtures Flashcards
What is an element?
Substances that can’t be split into anything simpler by chemical means. It contains only one type of atom.
What is a compound?
When two or more elements are chemically combined and are always in fixed proportion.
How do we seperate the elements in a compound?
With a chemical reaction.
What is a mixture?
Different elements or compounds not chemically combined together.
How can mixtures be seperated?
By physical means.
What kind of things melt and boil at a fixed temperature?
- Pure substances
- Elements
- Pure compounds
What happens to the melting and boiling point of mixtures?
They melt and boil over a range of temperatures.
How does the presence of impurities affect the melting and boiling points?
- They lower the melting point
- They raise the boiling point
What are physical separation techniques used for?
To separate mixtures.
What are the separation techniques used for?
- Simple distillation
- Fractional distillation
- Filtration
- Crystallisation
- Paper chromatography
What does insoluble mean?
That the solid won’t dissolve in a liquid.
What does soluble mean?
That the solid will dissolve in a liquid.
What is an aqueous solution?
It means that the substance is dissolved in water.
What is filtration?
It is used to separate an insoluble solid from a liquid.
What is the residue?
The substance left in the filter paper.
What is the filtrate?
The liquid that comes through.
What is an example of the substances that could be used in filtration?
Silver chloride (AgCI) and water (H2O).
What are the results found from using filtration?
The insoluble solid will be on top of the filter paper, and the liquid will be in the beaker at the bottom.
What is crystallisation?
It is used to separate a soluble liquid from a liquid.
(Solute from a solution).
What is an example of substances that can be used in crystallisation?
Sodium chloride and water.
How does crystallisation work?
The water evaporates and leaves behind the soluble solid in a crystal form.
How can you make crystallisation happen faster?
You can gently heat the solution to make the water evaporate faster.
What is simple distillation?
Used to separate a liquid from a solid when we want to keep the liquid.
How does simple distillation work?
We evaporate the liquid by heating it and then the vapour turns back into the liquid by condensing it.
What does the condenser do?
Turns the gas into a liquid.
What is an example of substances that can be used in simple distillation?
Obtaining drinking water from sea water.
What is fractional distillation?
Separates a mixture of liquids.
What needs to be special about the liquids?
They need to have different boiling points.
What does the fractionating column contain?
Glass beads.
How do the glass beads help in fractional distillation?
Their high surface area in the column help with the separation of the vapours.
What is chromatography?
It allows us to separate substances based on their different solubilities.
How does chromatography work?
The solvent makes its way up the paper and brings the ink with it.
What does the line on the chromatography paper have to be made out of and how much further up does it have to be from the bottom of the paper?
Pencil and 10cm up.
Why does it have to be pencil?
Because if it was pen, the ink would move up the paper with the solvent.
What does it mean if there are multiple spots?
It is a mixture of substances.
What does it mean if there is only one spot?
The substance is pure - only made up of one colour.
What is the solvent front?
The highest level of the solvent on the paper at any time.
What is the solvent usually made from?
A non-aqueous solution.
What affects the result found in chromatography?
- Their affinity (stickiness to the paper)
- How soluble they are (moves up the paper)
What is a chromatogram?
The pattern you get.
What does it mean if the dye doesn’t move?
It is not soluble in the solvent.
What does it mean if the dye moves too much up the paper?
It is too soluble in the solvent.
What does the retardation factor show?
It is a value to describe how far the spots move.
How do you work out the retardation factor?
Distance moved by a spot (from the pencil line) / Distance moved by the solvent front (from the pencil line)
