1.2 Amount of Substance

definition of mole

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

definition of relative atomic mass

Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12

definition of relative molecular mass

Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12

convert ^oC to K

+273

heating in a crucible - why it’s used

• method used for measuring mass loss in thermal decomposition reactions

• also for mass gain when reacting magnesium in oxygen

heating in a crucible - method

•Weigh an empty clean dry crucible and lid .

(lid improves accuracy bc prevents loss of solid from crucible, but should be loose fitting to allow gas to escape)

•Add 2g of hydrated calcium sulfate to the crucible and weigh again

•Heat strongly with a Bunsen for a couple of minutes

•Allow to cool

•Weigh the crucible and contents again

•Heat crucible again and reweigh until you reach a constant mass

(to ensure reaction is complete).

titration method

• rinse equipment

• touch surface of alkali with pipette ( to ensure correct amount is added)

• adds acid solution from burette

• •add a few drops of indicator and refer to colour change at end

• phenolphthalein [pink (alkali) to colourless (acid): at end point, pink colour just disappears] [use if NaOH is used]

• methyl orange [yellow (alkali) to red (acid): end point orange] [use if HCl is used]

• use white tile to help observe colour

• add acid to alkali while swirling mixture, dropwise at end point

• note burette reading before/adding acid

• repeat titration until 2 concordant results

% uncertainty equation

(uncertainty / (avg) measurement) x 100