C2: Fundamental Ideas (2)
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Ions
A charged particle produced by the loss/gain of electrons.
What sort of ions do metals form?
Positively charged ones. atoms lose electrons
What sort of ions to non-metals form?
Negatively charged ones. atoms gain electrons
Ionic Bonds
The electrostatic force of attraction between positively and negatively charged ions.
Relative Atomic Mass
The average mass of the atoms of an element compared with carbon 12.
Relative Formula Mass
The total of the relative atomic masses, added up in the ratio of the chemical formula of a substance.
Mole
The amount of substance in the relative atomic or formula mass in grams.
No of Moles =
Mass (g) / Ar or Mr
To calculate the percentage of an element in a compound:
> Work out the Mr of your compound, writing down the Ar of each element separately as you go. Divide the Ar of your element by the total Mr of the compound. x 100
To find an empirical formula:
> Divide the amount of each element by its Ar. Put what you get into a ratio. Divide all of them by the smallest no. in the ratio. Make a formula.
Total Mass of Products =
Total Mass of Reactants
Aqueous Solutions
Mixture made by adding a soluble substance to water.
Litmus + Acid
Red
Litmus + Alkali
Blue
Percentage yield of a chemical reaction =
amount of product produced/ maximum amount of product possible (x100)
Why might a percentage yield be less than it should be?
> Reaction might be reversible May have given unexpected products in alternative reactions. Some might be lost whilst handling apparatus. Lost during separation from reaction mixture.