3) Amount of substance Flashcards
Define amount of substance
the quantity whose unit of the mole, is used as a means of counting any species such as atoms, ions and molecules
Define Avogadro constant
the number of atoms per mole of the carbon-12 isotope (6.02 s 10^23 mol^-1)
What does the mass of 1 mole of atoms of an element equal?
the relative atomic mass in grams
Define molar mass, M
the mass per mole of a substance, in g mol^-1
State the equation linking n, M and m
n = m / M
Define molecular formula
the number of atoms of each element in a molecule
Define empirical formula
the simplest whole-number ratio of atoms of each element in a compound
What type of substance is the empirical formula especially important for?
those forming giant crystalline structures
Define relative molecular mass Mr
the weighted mean mass of a molecule of a compound compared with 1/12 of the mass of an atom of carbon-12
Define relative formula mass
the weighted mean mass of a formula unit of a compound compared with 1/12 of the mass of an atom of carbon-12
How do you calculate relative molecular mass Mr?
add together relative atomic masses of the elements making up a molecule
How do you calculate relative formula mass?
add together relative atomic masses of the elements in the empirical formula
Define analysis
investigating the chemical composition of a substance
Give the 2 steps for determining empirical formula from mass
- convert mass to moles using n = m / M
2. divide by the smallest whole number
Give the 2 steps for determining molecular formula
- work out empirical formula
- find the number of units in one molecule by dividing the relative molecular mass of the compound by the relative mass of the empirical formula
Many coloured salts are _ - which means they have water molecules / _ as part of their crystalline structure.
hydrated
water of crystallisation
Give 3 measurements and 5 steps for calculating the formula of a hydrated salt
measurements: mass of crucible, mass of crucible + hydrated salt, mass of crucible + anhydrous salt
1. heat the crucible + contents gently (1min) strongly (3min)
2. leave to cool
3. calculate the moles of anhydrous salt, mass and moles of water
4. find the smallest whole-number ratio of the moles calculated
5. write the value of x + the formula of the hydrated salt
State 2 assumptions taken when calculating the formula of a hydrated salt and how one can be corrected
all water has been lost -> heat to a constant mass
no further decomposition when heated
1cm^3 = _ml?
1
1dm^3 = _cm^3?
1000
_ ml = 1 litre?
1000
Give the equation linking moles, concentration and volume
n = concentration (mol dm^-3) x volume (dm^3)
Define standard solution
a solution of known concentration
Define molar gas volume Vm
the volume per mole of gas molecules at a stated temperature and pressure (24.0 dm^3 mol^-1 at RTP)