C2.1 Purity And Seperating Mixtures Flashcards
What is relative atomic mass?
The mean mass of an atom of an element compared to 1/12th of the mass of a carbon 12 atom
Define relative formula mass
The mean mass of a unit of a sub trance compared to 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 compound
How do you work out the empirical formula?
Divide by the HCF
How do you work out the empirical formula from percentages?
1) Divide each elements percentage by its mass number
2) Divide ALL the answers by the smallest answer
3) Write it out
Why do scientists use empirical formulas?
It makes little sense to write out formulas with huge numbers
What does pure mean?
A substance which consists of only one element or compound
What is a mixture
An impure substance made of more than one element or compound
Why are some mixtures useful?
Mixture can be useful for alloys which are a mixture of metals with more than one element. This adds strength and other beneficial qualities
How do you use melting points to distinguish between pure and impure?
Impure substances melt over a range of temperatures and the melting point is less than that of a pure substance, eg seawater has a lower melting point than pure water
The greater the difference, the more impure it is
Why should you heat a substance slowly and stir it?
It allows the temperature of the whole substance to increase evenly and mixing ensures that the whole thing is the same temperature
What is a solution?
a mixture formed when one substance dissolves in another
What is a solvent?
The substance a solute dissolves in
What is a solute?
The substance that dissolves in the solvent
What does soluble mean?
If a substance can dissolve in a solvent
What does insoluble mean?
If a substance cannot dissolve in a solvent