quantitative chemistry Flashcards
how do you calculate the percentage mass of one specific element in a compound
atomic mass x number of atoms
——————————————— x100
relative formula mass of compound
what is relative formula mass and how might it be written
sum of all atomic masses in a compound
Mr
what is avogadros constant (specific number)
6.02 x 10^23
what is a mole
the amount of a substance that contains 6.02 x 10^23 particles
(an avogadro number of particles)
relationship between moles and relative formula mass
mass (in grams) of one mole of substance/atoms = relative formula mass of the substance/atoms
e.g carbon Ar is 12
1 mol of carbon = 12g
formula triangle for mass, relative formula mass, ad number of moles
why might mass change in a chemical reaction?
Increase: one of the reactants is a gas and was not accounted in reaction vessel for reactants (e.g metal + oxygen —> metal oxide)
decrease: one of the products is a gas & it escaped
How do you workout the balanced equation only by knowing the masses of the reactants and products?
• work out Mr of each substance
• divide mass by Mr for each substance to find moles
• divide each by smallest number of moles in reaction
• write balanced equation with these whole big numbers
What is the limiting reactant?
The reactant that gets used up, same volume of product
How do you calculate mass of a product only using the mass of the limiting reactant and the balanced equation
• write out the equation
• calculate Mr of product and reactant you want
• calculate moles of the limiting reactant (mass/Mr)
• Look at ratio in equation, rearrange to substitute moles
how do you workout the volume of a gas?
Moles of gas x 24
what is atom economy?
Percentage of reactants forming useful product - the higher the “greener”
what does 100% yield entail?
You got all the products you expect to get - never occurs
Why is yield never 100%?
not all reactants react
There might be side reactions
You lose product when you try to separate it from the mixture
