C2.1 - Purity And Separating Mixtures Flashcards
What is relative atomic mass?
Mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom
What is the chemical formula?
How many atoms of each element there are in a unit of substance
What is relative formula mass?
The mean mass of a unit of substance compared to 1/12 the mass of a carbon-12 atom
What is an empirical formula?
The simplest whole-number ratio of the atoms of each element in a substance
What does pure mean?
A substance that consists of just one type of substance
Are all mixtures pure or impure?
Impure
What does impure mean?
A substance that contains more than one element or compound
What is an alloy?
A mixture of a metal with one or more elements
How does melting point tell us if a substance is pure/impure?
Its melting point is less than that of the pure substance
Melts at a range of temperatures
The temperature of a substance remains … when it melts
Constant
What is a solute?
A substance that dissolves
What is a solvent?
A substance that a solute dissolves in
What is a solution?
The product formed when one substance dissolves in another
TRUE OR FALSE?
Substances can be soluble in one substance but insoluble in another substance?
True
What does filtration do?
Separates an insoluble substance in its solid state from substances in the liquid state
How does filtration work?
A solution is poured into filter paper
The tiny holes in the filter paper allow the liquid to pass through as the filtrate whilst leaving the solid behind as the residue
In filtration, what is the name of the solid left behind by the filter paper?
Residue
In filtration, what is the name of the liquid that passes through the filter paper?
Filtrate
What does crystallisation do?
Separates the solute from the solvent
How does crystallisation work?
When you heat the solution, the solvent evaporates, leaving the solute behind
Why does crystallisation take a long time?
It needs to be gently heated until it becomes a saturated solution
What does simple distillation do?
Separates the solvent from the solution
How does simple distillation work?
The solution is heated, the solvent boils to escape the solution in gas state.
Cooled and condensed back into liquid state in another container by condenser
What does simple distillation rely on?
The solvent having a much lower boiling point than the solute
What does fractional distillation do?
Separates two or more substances from a mixture in liquid state
How does fractional distillation work?
The two substances with the lowest boiling points boil into the fractionating column, where they condense and separate
What does fractional distillation rely on?
The substances having very different boiling points
What does chromatography do?
Separates mixtures of coloured compounds
What are the two phases of chromatography?
Stationary phase - does not move
Mobile phase - does move
What is the stationary phase in TLC Chromatography?
Thin layer of silica or aluminum powder
How do you calculate Rf value in chromatography?
Distance travelled by substance
___________________________________
Distance travelled by solvent
Why is an element like nitrogen used as the mobile phase in gas chromatography?
It is a noble gas, so it is unreactive with the sample
In gas chromatography, how do we tell which component bonds strongest to the stationary phase?
How fast it travels through the column
What are the advantages of using TLC over Paper chromatography?
Quicker
More sensitive, so smaller samples can be used
Larger range of stationary phases and solvents to choose from
What separation method should you use when separating insoluble and soluble substances?
Filtration
What separation method should you use when separating a solute dissolved in a solvent?
Crystallisation
What separation method should you use when separating a liquid from the solution?
Simple distillation
What separation method should you use when separating two or more liquid substances?
Fractional distillation
What separation method should you use when separating coloured soluble substances?
Paper chromatography
Thin-layer chromatography
What is formulation?
Mixtures where the ingredients are combined in exact amounts
