1b Elements, compounds and mixtures Flashcards
What is an element?
A substance that cannot be broken down into simpler substances by chemical methods
What is an atom?
The smallest part of an element that can exist on its own
What is a molecule?
A combination of atoms
What is a compound?
A substance containing two or more elements joined together
What is a mixture?
Different substances but not chemically joined in any way
What is chromatography?
Separation technique used to separate the colours in dyes and inks that relies on the affinity of components of a mixture to a mobile phase and a stationary phase
The colours with a higher solubility will spread further than others - they will have a higher Rf value for that solvent
If the dye doesn’t move at all that means it insoluble in that solvent
What is the mobile phase?
This is the phase that is a carrier for the components as they travel through the stationary phase
Solvent + (water, ethanol)
What is the stationery phase?
This is the phase that is stationery
Paper
How to calculate Rf values?
- Distance travelled by component
- Distance travelled by mobile phase
- Specific to each plate
- Comparable
- Each component on the plate has unique Rf value
Rf = distance travelled by dye/distance travelled by solvent
Rf = 2.1/2.8 = 0.75
What is a mixture?
Different substances but not chemically joined in any way
What is a solution?
The mixture formed when a solute is dissolved in a solvent
What is a solvent?
The thing that does the dissolving
eg. water and ethanol
What is a solute?
The thing that is dissolved
eg. salt
What does soluble mean?
Is a solid that can be dissolved (disappears) in a solvent eg. sugar
What does insoluble mean?
A soli which is not soluble
eg. sand
What is the filtrate?
Is the liquid part of a mixture that is filtered
What is residue?
Insoluble solid that is left in filter paper
What is distillate?
The liquid that evaporates and condenses as a result of distillation
What is crystallisation?
Crystals left when the saturated solution is left to evaporate slowly
What is distillation?
A method used to separate a liquid from the solids dissolved in it
Distillation = Evaporation + Condensation
What is simple distillation?
Simple distillation is used to separate the solvent and solute in a solution in order to collect the pure solvent.
The solution is put in a flask with anti bumping granules to allow smooth boiling.
The heat from the Bunsen burner evaporates the solvent. The vapour then rises and enters the Liebig condenser.
The condenser cools the vapour to turn it back into a liquid. This pure liquid is called the distillate
What is fractional distillation?
Fractional distillation separates mixtures of two or more miscible liquids (liquids that mix). For example, ethanol and water.
The mixture is heated in a flask with anti-bumping granule. Both liquids evaporate and their vapour enters the fractionating column. The column has a temperature gradient which is hotter near the bottom and cooler near the top.
Because ethanol has a lower boiling point it quickly rises up the column, enters the condenser and condenses back to a liquid. Water has a higher boiling point, so it condenses near the bottom of the fractionating column and remains in the flask.
