Quantitative Chemistry Flashcards
Conservation of Mass
No mass is lost or gained during a chemical reaction - no atoms lost or gained
Relative Atomic Mass - Ar
Average mass of the isotopes of an element compared with 12g or Carbon - 12
Relative Formula Mass - Mr
Sum of relative atomic masses of all atoms shown in the formula
How to calculate Mr
Look up Ar for each atom and add them together - count small no.s
Mole
Ar in grams, contains the same no of particles (6.02 x 10²³)
How to calculate number of moles of an atom
mol = mass / Mr
Calculate the amounts of substances in equations
- Work out moles of what you are given
- work out moles of what you are finding using ratio
- convert moles to mass
Using moles to balance equations
Work out moles for reactants and products, write in a ratio then use to balance the equations
Limiting Reactant
Reactant that is used up first in a chemical reaction - limits the amount of product made
How to work out limiting reactant
Look at the moles (divide moles by big number if necessary) see which is limiting
Percentage yield definition
Percentage yield of a chemical reaction shows how much product was actually made compared with the amount of product that was expected
Why might there be less yield than expected?
- loss of product
- incomplete reaction
- impure reactants
- other products were made
Percentage yield formula
%yield = actual/theoretical yield
Atom economy and why is it useful
A measure of the amount of starting materials that end up as useful products - saves money; more sustainable
Atom economy formula
Mr of desired products/total mr of reactantsf
