C4-Chemical Calculations Flashcards
How do you work out relative formula mass (Mr)
Add up the atomic number (big number) of all the atoms in the molecule
What is avogadros number
6.02×10^23
How do you work out moles
Mass÷Mr
Reasons the yield of a chemical reaction rarely being 100%
If the reaction is reversible it may not go to completion
There may be a side reaction
Some yield may be lost when the product is transferred from the reaction vessel
How do you calculate % yield
Mass of products ÷ mass of theoretical products × 100
How do you work out atom economy
Relative formula mass of desired product ÷ sum of the relative formula masses of the reactants × 100
Why is a low atom economy bad
A lot of reactant is wasted, and this costs money
The waste product has to be disposed of. This can be expensive, so some companies try to get around this by reusing the waste product
What is the limiting reactant
The reactant that is used up first in a chemical reaction
What are titration used for
To find unknown concentration of a solution
