Stoichiometry

the number and type of atoms in one molecule

Add the atomic masses of the atoms in the molecule - don’t forget if there’s a small number below the element you need to multiply its atomic mass by that number

count the atoms of each element, then write the chemical formula using the element symbols and subscripts to indicate the number of each ato

first write the balanced symbol equation, then add state symbols (s, l, g, aq) to indicate the physical state of each substance, and finally, for ionic equations, identify and represent only the ions that participate in the reaction

Atomic mass

Ar = ( %1 * mass1 ) + ( %2 * mass2 ) / 100

% yield = actual mass of product made / theoretical mass * 100

% purity = mass of pure substance / total mass * 100

m/mr

C = n/v

V of gas = n * 24 dm3

divide by 1000

Aqueous

1 - split all ions (in aqueous form) 2 - write out charge and state of all ions 3 - cross out ions which are equivalent on both sides of the reaction (theses are the spectator ions) 4 - ionic equation is everything left over

• convert the given percentages or masses of elements into moles ( % or mass / atomic mass Ar ) • divide each by the smallest number of moles to get a whole-number ratio

Water and salt

Hydrogen + salt

Metal oxide

Salt + water + carbon dioxide

Hydrochloric acid - HCl Sulfiric acid - H2SO4 Nitric acid - HNO3

-OH

SO4 2-

Mass cannot be created or destroyed

1 - calculate the number of moles 2 - compare as a ratio of moles : find the simplest ratio 3 - whichever is greater is the reagent in excess, other is limiting