C2.1 Flashcards
What is relative atomic mass?
Relative atomic mass, At, is the mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom.
What is relative formula mass?
Relative formula mass, Mt, is the mean mass of a unit of a substance compared to 1/12 the mass of a carbon 12 atom.
What does empirical formula show?
The simplest whole-number ratio of the atoms of each element in a compound.
What does a balanced chemical equation show?
The formulae and number of units for all the substances in a reaction.
What is a pure substance?
an element consisting of just one element or compound.
What is a mixture?
A mixture is an impure substance, since they contain more than one element or compound.
What is special about the melting point of a pure substance?
It is a single temperature
What happens to the melting point if a substance is impure?
If a substance if impure, its melting point is less than a pure substance and it is over a range of temperatures.
How does a solution form?
when one substance is dissolved in another.
What is the solute?
The substance that dissolves
What is the solvent?
The substance that the solute dissolves in.
What does filtration do?
Filtration separates an insoluble substance in the solid state from another substance in the liquid state.
How do you do crystallisation?
Heat a solution, let the solvent evaporate, leaving the solute behind. If you heat it too strongly, you get a powder, but if you allow the solvent to evaporate slowly, you get regularly shaped crystals.
What is simple distillation?
Separates a solvent from a solution, when the solution is heated, the solvent boils but the solute doesn’t. The solvent evaporates, then is cooled and condensed by a condenser.
What does fractional distillation do?
Separates two or more substances from a mixture in the liquid state.
What are the stationary and mobile phases in paper chromatography?
stationary phase= absorbent paper and mobile phase= solvent in liquid state
What are the stationary and mobile phases in thin layer chromatography?
Stationary phase=a thin layer of silica or alumina powder spread over a plate of glass or plastic.
mobile phase= solvent in liquid state.
Describe gas chromatography
gas chromatography separates the components of a mixture and also measures their amounts. Stationary phase= silica/alumina powder packed into metal column and mobile phase= unreactive carrier gas(e.g: nitrogen)
What is the formula for Rf
Rf= distance travelled by substance/ distance travelled by solvent
Describe Rf values
Rf values always vary from 0 to 1 and have no units.
Why is TLC better than paper chromatography?
its quicker, more sensitive(smaller sample used); larger range of solvents and stationary phase; can scrape dots for further analysis.
What separation methods should be used if the mixture contains insoluble and soluble?
dissolving and filtration.
What separation methods should be used if the mixture contains a solution?
crystallisation and simple distillation
What separation methods should be used if the mixture contains 2 or more liquid substances?
fractional distillation
What separation methods should be used if the mixture contains coloured soluble substances?
paper chromatography or thin layer chromatography.
