3.1.2 Amount Of Substance Flashcards
What is relative atomic mass?
Average mass of one atom / 1/12 mass of one carbon-12 atom
What is relative molecular mass?
Average mass of one entity / 1/12 mass of one carbon-12 atom
What is Ar?
Relative atomic mass
What is Mr?
Relative molecular mass
When is relative formula mass used?
When a compound is ionic
What is Avogadro’s constant? (2)
The number of particles in one mole
6.023 x10^23
What is the molecular formula?
The actual whole number of atoms of each element in a molecule of a compound
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound
How is the empirical formula of a compound calculated? (3)
Divide proportions of elements by their respective Ar
Divide these values by the smallest
Multiply the calculated values by a number that makes all of them as near to a whole number as possible
How is the molecular formula calculated from an empirical formula? (3)
Calculate the ‘empirical mass’ from the given formula
Divide the molecular mass by the empirical mass
Multiply the ratios of the empirical formula by this value to make the molecular formula
How is the number of moles calculated?
Mass given (g) / Mass of one mole (Mr)
How is the number of particles calculated?
Number of moles x Avogadro’s constant
How is the mass of one particle calculated?
Mass of one mole (Mr) / Avogadro’s constant
How is concentration/molarity calculated?
Concentration (moldm^-3 / gdm^-3) = mass (mol/g) / volume (dm^3)
How is the limiting factor of an equation calculated? (2)
Calculate the number of moles of the desired product that would form with each given mass of reactant
The reactant that makes the least product is the limiting factor
How is the volume of gas calculated?
pV = nRT p = pressure (Pa) V = volume (m^3) n = number of moles R = Rydberg's constant (8.31 J K^-1 mol^-1) T = temperature (K)
What assumptions does the pV = nRT equation rely on? (2)
Particles are treated as hard spheres of negligible size
Particles experience no attractive forces
How is atom economy calculated?
(molecular mass of desired product) / (sum of molecular masses of all reactants) x 100
What are the advantages of a high atom economy? (5)
Efficient use of raw materials Less waste to be disposed of Less harmful to environment More sustainable Easier and cheaper process so products are cheaper and more accessible
What is atom economy?
A measure of the proportion of reactant atoms that form the desired product
What is theoretical yield?
The mass of product that should form, assuming no chemicals are ‘lost’ in the process and the reaction is fully completed
How is percentage yield calculated?
(actual yield) / (theoretical yield) x 100
Why is the actual yield always lower than the theoretical yield? (3)
Not all starting chemicals react fully
Some chemicals are ‘lost’ (e.g. left on filter paper, side reactions)
Reaction may be reversible
How is density calculated?
Density (g cm^-3 / g mL^-1) = mass (g) / volume (cm^3 / mL)
