Stoichiometry Flashcards
What is the relative atomic mass?
The weighted average mass of all the isotopes
(Mass number x percentage) + (Mass number x percentage) etc… / 100
What is the relative formula mass?
The mass of all the atoms together in a molecules. Add all the Ars together
What is the equation for the number of moles?
Number of moles = mass / mass of 1 moles(Ar/Mr)
What is Avogadro’s constant?
One mole of anything will contain the same number of particles
How do you work out the percentage composition?
(Num. of moles of element x Ar x 100) / Mr of compound
How do you work out the mass of one substance in a reaction from the mass of another?
1) check that e.q. Is balanced
2) write in all info given
3) calculate the moles of substance which has the mass given
4) use the mole rations to find the number of moles of the unknown substance
5) use ‘the triangle’ to find the mass of the substance from the Mr and moles
What is the empirical formula?
The formula of a substance that shows the simplest whole number ratio of an element in a compound
How do you work out the empirical formula?
1) write out them masses of each substance
2) using the Mr, work out the number of moles of each substance
3) divide all by the lowest number of moles
4) try to find a ration from these numbers
What is percentage yield?
The overall success of an experiment
(Actual yield x 100) / predicted yield
Why can’t we have 100% yield?
- reaction is reversible
- some left in filtration
- some left over when transferring liquids
- unexpected reactions
How do you work out the atom economy?
(Total Mr of useful products x 100) / total Mr of reactants
What is the molecular formula?
The ‘true’ formula of a compound
Mr/ empirical formula mass x empirical formula
E.g. Empirical formula is NH2. Mr = 32
32/16 = 2. 2 x NH2 is N2H4
What is Avogadro’s law?
At the same temp and pressure, equal volumes of all gases contain equal numbers of moles
Num moles = vol dm^3 at RTP / 24
Num moles = vol cm^3 at RTP / 24000
