amount of substance (mass) Flashcards
define empirical formula
the simplest whole number ratio of atoms of each element in a compound
e.g C3H6 (molecular) -> CH3 (empirical)
how do you convert from atoms to moles (and vice versa)
atoms to moles: divide by Avogadro’s constant
moles to atoms: multiply by Avogadro’s constant
what is the equation for calculating amount of substance (n)?
n (moles) = mass (g) / Mr “Molar Mass” (g mol -1)
How do you calculate the water of crystallisation using total Mr?
x = (Mr total - Mr Salt) / Mr H2O
what is molecular formula?
the number of atoms of each element in a molecule
define amount of substance (n)
a quantity used to count the number of particles in a substance
define mole
the unit used to measure amount of substance (n). one mole is the amount of a substance that contains 6.02 x 10*23 particles
what is Avogadro’s constant?
6.02 x 10*23 mol-1, the number of particles in each mole of carbon-12
define molar mass
the mass per mole of a substance
unit g mol-1
the same as relative atomic masses in grams
what is a hydrated salt?
a (usually) coloured salt which contains water molecules
what is the water of crystallisation?
the water in the crystalline structure of a hydrated salt
what is an anhydrous salt?
usually a white powder, water has been removed and so the crystalline structure is lost
how do you calculate empirical formula from abundance data?
- convert percentage by mass into moles of atoms using n = m(%)/Mr
- divide by the smallest whole number
how do you calculate molecular formula from the empirical formula?
- find the empirical formula
- find the relative mass of the empirical formula
- find the number of units in one molecule (relative molecular mass/relative empirical mass)
- multiply the empirical formula by the number of units
how do you calculate molecular formula from Mr?
multiply each element in the empirical formula by x (xH2O- water of crystallisation)
