SC5i - MASS CALCULATIONS Flashcards
relative formula mass / RFM / Mr definition
mass of all atoms in a formula
how to calculate RFM
sum of (number of atoms of each element x relative atomic mass (RAM) of element)
molecular formula definition
normal formula showing the ratio of elements in a compound
always a MULTIPLE of the empirical formula
empirical formula
the simplest whole number ratio of elements in a compound
always multiplies to make the molecular formula
concentration definition
amount of solute (in g) dissolved in 1dm³
1dm³ = _L = _cm³
1dm³ = 1L = 1000cm³
to convert cm³ to dm³, divide by ____
1000
formula for concentration
concentration = amount of substance (g) / volume (dm³)
law of conservation of mass
in a chemical reaction particles are not created or destroyed
mass of all particles at the start of a reaction = mass of all particles at the end of a reaction
mole definition
the amount of substance that contains the Avogadro number (6.022x10²³) of particles
formula for moles
moles = mass / RAM or RFM
formula for number of particles
particles = moles x Avogadro number
steps of reacting mass calculations
reacting mass calculations involve calculating a mass of something (either a product or reactant) given the mass of other things
1. write a balanced equation for the reaction
2. use the information given to calculate the moles of something using the equation moles = mass / RFM
3. used the balanced equation to find the moles of so,etching else
4. find the mass using the equation mass = moles x RFM
stoichiometry definition
ratio of moles of each substance in an equation
how to calculate stoichiometry
if you know the mass ratios in an equation, you can calculate the stoichiometry by dividing by the RAM or RFM of each substance
A : B =
mass of A / RFM of A : mass of B / RFM of B
