Quantitative Chemistry Flashcards
what is a mole
a unit of an amount of substance (6,.02 x 10 power of 23)
A mole contains the same number of particles as what
12g of carbon-12 (6.02 x 10 power 23)
How to find the formula mass (Mr) of a compound
add the atomic mass of each element (times by the small number before adding if there is one)
How to find the value of “x” in a hydrated salt formula E.g. the value of x in CuSO4.xH2O if the total Mr of the compound is given.
calculate the mass before and after the reaction. Then, find the difference between them and divide it by 18 ( the Mr of H2O)
how to calculate the number of moles in a substance
moles = mass/Mr
How to calculate the mass of a substance if the number of moles is given
mass = moles x Mr
How to calculate the mass of a reactant/product if the mass of a different reactant/product in the equation is given by using molar ratios (reacting masses).
find the moles of the compound given - use ratio - times by Mr of compound you are trying to find out
what is molecular formula
the actual number of atoms of each element present in a molecule or compound
what is the empirical formula
the simplest whole number ratio of atoms present in a compound
How to find the empirical formula of a compound if its molecular formula is given
Simplify the ratio of elements in the molecular formula
Calculate the empirical formula of a compound if the mass or % mass of each element within it is give.
find the moles of each element in the compound using the mass ( if percentage, pretend it is a mass) - divide the largest by the smallest - make the results into a ratio if not already - use ratio to write out formula
How to work out the molecular formula of a compound using its empirical formula and Mr
Find the mr of the empirical formula
Then, divide the Mr of the molecular formula by the Mr of the empirical formula
Then times the number (answer from the last step) by each number in the empirical formula x2
e.g: N1 Al3 O2 —–> N2 Al6 O4
This is your molecular formula
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Calculate the percentage yield of a substance
% yield = actual yield/theoretical yield x 100
Identify reasons why percentage yield is rarely 100%
The reaction is incomplete
The possibility of side reactions (formulation of bi-production)
Product transfer losses
How to identify which substance is in excess and which is the limiting reactant in an equation when told the moles of each.
the substance in excess is the one that moles are lower when made the same ratio
