C2.1 Flashcards
What is relative atomic mass
Relative atomic mass is the mean mass of an atom compared to 1/12 the mass of a carbon 12 atom.
What is relative formula masss
Relative formula mass (Mr) is the mean mass of a unit of a substance compared to1/12 of the mass of a carbon 12 atom.
What is an empirical formula
An empirical formula shows the simplest whole number ratio of the atoms of each element in a compound.
What does a balanced chemical equation show
A balanced chemical equation shows the formulae and number of units for all the substances in a reaction.
What does a pure substance consist of
A pure substance consists of just one element or compound.
Are mixtures pure or impure
Mixtures are impure as they contain more than one element or compound.
Why are mixtures useful
Mixtures are useful because they contain the properties of all the substances that are in them.
What is the melting point of a pure susbtance
The melting point of a pure substance is a single temperature.
What happens if a substance is impure
If a substance is impure then the melting point is less than that of a pure substance. The substance also melts over a range of temperatures not just one.
How do you determine the melting point of substances
You determine the melting point of a substance by heating it. You then measure its temperature at regular time intervals and then plot a graph.
How do you make the process to find melting points more accurate
Heat it slowly
Stir the substance as it melts
What is a solute
The substance that dissolves
What is a solvent
The substance it is dissolved in
What does filtration do
Filtration separates an insoluble substance in the solid state from substances in the liquid state. It works because, the filter paper has small holes in it that the liquid pass through but not the insoluble substance.
What is the equipment needed for filtration
A funnel, a conical flask and filter paper.
What are the substances that are separated in filtration
The residue is the insoluble substance and collects in the filter paper.
The filtrate can pass through the filter paper and collects in the conical flask
What is crystallisation
Crystallisation is when you heat a solution and the solvent evaporates leaving the solute behind and if you allow the solvent to evaporate slowly you get regularly shaped crystals.
What is needed for crystallisation to occur
For crystallisation to occur you need to heat the solution slowly until it becomes a saturated solution (no more solute can be dissolved in the solvent at that temperature) crystals will the start to form.
What is the equipment needed for crystallisation
An evaporating basin, a beaker with water, the solution and bunsen burner
What does simple distillation do
Simple distillation separates a solvent from a solution. It relies on the solvent having a much lower boiling point than the solute. When the solution is heated the solvent boils but the solute doesn’t. The solvent escapes in the gas state and is condensed back into liquid by the condenser.
What is the equipment needed for simple distillation
A condenser, test tube, thermometer and conical flask
What is fractional distillation
Fractional distillation separates two or more substances from a mixture in the liquid state. It relies on each state having a different boiling point and uses a fractionating column.
In the fractionating column:
. the water vapour condenses on the inside surface heating it up
. when the temperature inside reaches the lowest boiling point of one of the liquids, it can’t condense anymore so it passes into the condenser whereas the other liquid falls back into the flask.
What is the equipment needed for fractional distillation
Fractionating column, conical flash, beaker, thermometer, condenser
What does chromatography rely on
Chromatography relies on two different chemical phases.
. a stationary phase that doesn’t move
. a mobile phase that does move
How do scientists compare the different values
They use the Rf values.
How is gas chromatography different to paper and thin layer chromatography
Its different as the mobile phase is an unreactive carrier gas and the stationary phase is silica or alumina powder.
Why do substances take different times to pass through
Because it depends on how attracted it is to the stationary and mobile phase.
Rf formula
Rf = distance travelled by substance/distance travelled by solvent
When the mixture contains an insoluble and soluble substance what do you do
Dissolving followed by filtration
When the mixture contains a solute dissolved in a solvent what do you do
Crystallisation to obtain the solute or simple distillation to obtain the solvent
When the mixture contains two or more substances in the liquid state
Fractional distillation
When the mixture contains a coloured soluble substance
Paper chromatography or thin layer chromotography
What are the benefits of paper chromatography
It is quicker
It is more sensitive so smaller samples can be used
There is a larger range of stationary phases and solvents to use
