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)
Give the equation linking moles, volume and molar gas volume
n = volume / molar gas volume
Give the ideal gas equation with units
pV = nRT
pressure (Pa) x volume (m^3) = amount of gas molecules (mol) x ideal gas constant (8.31Jmol^-1 k^-1) x temperature (K)
cm^3 -> m^3?
x 10^-6
dm^3 -> m^3?
x 10^-3
°C-> K?
+ 273
kPa -> Pa?
x 10^3
Define stoichiometry
the ratio of the amount, in moles, of each substance in a chemical equation
Give 1 key piece of apparatus and 3 steps for identifying an unknown group 2 metal
gas syringe
1. calculate moles of H2 collected
2. calculate amount of metal X using the equation:
X(s) + 2HCl(aq) -> XCl2(aq) + H2(g)
1 : 1
3) calculate the relative atomic mass and compare to the periodic table
Define theoretical yield
the yield resulting from complete conversion of reactants into products
Give 3 reasons why the theoretical yield is difficult to achieve
reaction not going to completion
other side reactions
purification resulting in the loss of some product
Define actual yield
the amount of product obtained from a reaction
Give the equation for percentage yield
percentage yield = (actual yield / theoretical yield) x 100%
Define limiting reagent
the reactant that is not in excess, which will be used up first and stop the reaction
How can you identify the limiting reagent?
calculate moles of each reactant and compare with the equation
Give the equation for atom economy
atom economy = (sum of molar masses of desired products / sum of molar masses of all products) x 100%
Reactions with high atom economies will produce _ and few _ - making _ use of natural resources. However, sustainability / efficiency will also depend on _.
large proportion of desired products
unwanted waste products
best
percentage yield
