Calculations Involving Masses Flashcards
what is relative formula mass, Mr,
the sum of the relative atomic masses of all the atoms shown in the formula
what is avagadro constant
6.02 x10^23, whihc is the number of atoms, ions or molecules in one mole of a substance
number of moles of a substance =
mass(g) / molar mass
atoms =
moles x 6.02 x 10^23
percentage of an element in a compound
(number of atoms of that element x Ar) / molar mass of the compound x 100
volume of gases =
moles x 24
1 dm^3 =
1000cm^3
concentration of solution =
moles / volume
concentration in g dm^3 =
concentration in mol dm^3 x molar mass
concentration in g dm^3 =
mass of solute / volume
what is empirical formula
the simplest whole number ratio of each element in a compound
how to find empirical formula
1) mass / Ar
2) amount / smallest amount
when does a reaction have a high atom economy
when more of the starting materials end up as useful products
why is it important to use reactions with high atom economy
there is less waste
fewer reactants are used/needed
the process is more sustainable because it conserves natural resources
atom economy =
Mr of useful product / sum of relative formula masses of all the reactants x 100
how do you improve the atom economy of a reaction
find uses for the by products of the reaction
percentage yield =
actual yield / theoretical yield x 100
what are the reasons why the actual yield is less than the theoretical yield
- some of the product is lost when it is seperated from the reaction mixture
- there may be unwanted side reactions taking place which compete with the main reaction
- the reaction may not go to completion possibly because the reaction has not been left for long enough or the reaction is reversible and reaches equilibrium
why is excess reactant to used
to make sure all the acid completely reacts
why is excess reactant to used
to make sure all the acid completely reacts
