principles - chemical formulae, equations and calculations

without all the experiments from the moles test

what is Mr

relative molecular mass (sum of Ar)

what is Ar

the atomic mass - from periodic table - protons + neutrons

what is Mr

the molecular mass - sum of Ars

define mol

the unit for amount of a substance

mass = ___ x ___

mass = Mr x moles

percentage yield = ___ / ____ (x____%)

percentage yield = actual yield (g) / theoretical yield (g) x100%

why would you get less product than theoretically (3)

• loss of reactants in transfer

• side reactions

• some reactions are reversible, they reverse

  • not everything reacted under heat ()

define empirical formula

the simplest whole number ratio of atoms in a compound

how to find empirical formula (Mg - 2.4, O - 1.6) the table

	Mg	O
mass	2.4	1.6
Ar	24	16
moles	0.1	0.1
ratio	1 (divide all by smallest number)	1

what is molecular formula

the actual number of atoms of each element in a molecule of the compound

general, how to find molecular formula

first find empirical formula

find Mr of empirical formula, compare that with given Mr of molecular thing

always a multiple of the empirical, what needs to be multiplied up

concentration moles formula

moles = concentration (mol/dm3) x volume (dm3)

gas volume moles formula

moles = gas volume (dm3) / 24

1 mole takes up 24dm3 at room tempw

how to go from mol/dm3 to g/dm3 and vice versa

the logic also

• To go from g/dm³ to mol/dm³: Divide by the molar mass in grams

• To go from mol/dm³ to g/dm³: Multiply by the molar mass in grams

why do all gasses 1 mole = 24dm3

because the volume is essentially the same as the particles are so small their actual size is negligible, space in between creates the volume

24 dm3 in cm3

24 000 cm3

concentration formula with mass - g/dm3 conc.

how to find excess reagent, general steps

chemical formula is the correct one

compare formula moles with moles used in experiment

compare the ratios - where one reactant is ‘used more‘ in the experiment than in the formula, it is in excess

same if there is not enough of one irl reactant vs the ratio, that’s the limiting reagent so the other is in excess

Mg + 2Hcl → MgCl2 → H2O

0.3 mol reacts with 0.3 mol of Hcl, which is in excess

check notes

its Mg in Excess