Quantitative Flashcards
what is the principle of conservation of mass?
no atoms are lost or made during a chemical reaction - mass of products = mass of reactants
what is occurring if there appears to be a mass change in a reaction?
reactant or product may be a gas and its mass has not been taken into account e.g. in a reaction of a metal and oxygen or thermal decomposition
how do you calculate % yield?
actual yield / theoretical yield * 100
why is % yield never 100%?
- reaction may not go to completion (eg if reaction is reversible)
- reactants may be impure (may react in different ways)
- some product lost to equipment when separated from reaction mixture (left behind on apparatus)
define atom economy
how much of the total mass of reactants is converted into the desired product
what does a high atom economy mean?
less waste - may have high % yield but low atom economy
how do you calculate atom economy?
sum of Mr of desired product / sum of Mr of all reactants x 100 (use coefficients to calculate Mr as finding out number of atoms)
how do you calculate relative atomic mass (Ar)?
weighted average mass of all isotopes = (mass of isotope 1 x % of I1) + (mass of I2 x % of I2) / 100
how do you calculate relative formula mass (Mr)?
sum of relative atomic masses (Ar) in a formula
how do you calculate % composition?
(Ar*number of atoms) / Mr * 100
what is a ‘mole’?
unit of measurement - 1 mole of any substance contains the same number of the stated particles, atoms, molecules or ions as 1 mole of any other substance
give Avogadro’s constant
6.022 x 10^23
what is the mass of 1 mole of a substance in grams numerically equal to?
its Ar or Mr
how do you calculate the number of particles?
moles x 6.022^23 (x no. atoms)
how do you calculate moles?
mass / relative formula mass (N=m/Mr)
concentration * volume (N=cv)
volume of a gas / molar volume (24) (N=v/24)
