C4: Quantitive Chemistry Flashcards
What is the relative atomic mass, Ar, of an element?
An average mass if the isotopes of that element weighted to take into account the abundance of each isotope.
What is the relative formula mass, Mr, of a compound?
The sum of the relative atomic masses of the atoms in the numbers shown in the formula.
What is a mole and what is it’s value?
1 mole = 6.02x10²³ atoms
The Ar of any element = 1 mole of it
What is the formula for the number of moles in an element?
Number of moles = Mass / Ar or Mr
(g)
Ar for elements
Mr for compounds
How are the number of moles in a compound calculated?
Moles = Mass / Total Mr
What is Avogadro’s constant?
The value of 1 mole
How do you calculate the number of moles of atoms in one mole of a compound?
Every atom accounts for 1 mole, so just count them
How do you calculate the number of atoms in a compound?
Moles = Mass / Mr
Then moles * 6.02x10²³ = number of atoms
How do you calculate the amount of product produced with a given mass of a reactant?
Work out number of moles of each by calculating the moles of the reactant (moles = mass/Mr), then the product, which will have a proportionate number of moles
Then do mass = number of moles * Mr of product
What is the limiting reactant?
A reactant that’s completely consumed after a chemical reaction
What is the excess reactant?
The reactant that’s not entirely used up
How do you calculate the moles produced, taking into account the moles of reactants used?
The moles of product produced will be the same as the smallest number of moles of one of the reactants
What is the formula for concentration?
concentration = mass / volume
(g/dm³) (g) (dm³)
How can concentration be changed?
If the mass of the solute is increased (with vol. kept the same) conc. is increased.
If vol. is increased (mass of solute kept the same) conc. is decreased
What is the formula for % yield?
% yield = (mass of useful product/ maximum theoretical mass of product)*100
Why is it impossible to achieve 100% yield?
Some product is lost when separated from the mixture (as residue on containers)
Reversible reactions may not be completed
Some reactants react unexpectedly, so weird products are made (impurities?)
What is atom economy and how is it calculated?
The % of useful products produced from reactants
Atom economy = (Mr of desired products/ sum of Ar of all reactants)*100
What’s the importance of atom economy?
By minimising waste product, money is saved
Sustainability is increased from reduced waster
What is another measure of concentration of a solution?
Calculate the number of moles in a given vol.
Conc = moles/volume
(mol/dm³) (dm³)
What is the conversion between dm³ and cm³?
1dm³ = 1000cm³
What is the volume of 1 mole of any gas?
24dm³
At room temp (20C) and 1atm
