1.3 chemical calculations Flashcards
what does the term relative atomic mass mean
the average mass of one atom of an element relative to 1/12th the mass of an atom of carbon-12
what does the term relative formula mass mean
the weighted average of the masses of the formula units compared to 1/12th the mass of an atom of carbon-12
what does the term relative isotopic mass mean
the mass of one atom of an isotope compared to 1/12th the mass of an atom of carbon-12
what is mass spectrometry
mass spectrometry is a type of analytical technique which measures the mass to charge ratio of ions. it also measures how abundant each ion is so it can be used to calculate the relative atomic mass
define empirical formula
the simplest whole number ratio of atoms of each element in a compound
define molecular formula
the actual number of atoms of each present in a compound
define the Avogadro constant
the number of particles in one mole of a substance. this is 6.02 x 10^23 particles
what is the equation linking Avogadro’s constant to moles
number of particles =
moles x Avogadro’s constant
define molar mass
the mass per mole of a substance measured in g mol-1
what is the equation that links moles to mass
moles =
mass(g) x relative atomic mass
define concentration
the amount of moles per unit volume
how can concentration be calculated in g/dm^3
concentration =
mass (g) / volume (dm^3)
how can concentration be calculated in mol/dm^3
concentration (mol/dm^3) =
moles / volume
what is the molar volume of any gas at room temperature and pressure
24 dm^3
how is molar volume at a given pressure affected if temperature is increased
an increase in temperature reduced the molar volume at a given temperature
how is the molar volume affected if the pressure is increased
an increase in pressure will mean the maximum molar volume reduces. up to this maximum, increasing the pressure will increase the molar volume
what is the ideal gas equation
pV=nRT
p - pressure (pa)
V - volume (m^3)
n - number of moles
R - gas constant (8.31 J K-1 mol-1)
T - temperature (K)
how can percentage yield be calculated
percentage yield =
(actual yield / theoretical yield) x 100
why might the actual yield of product be less than expected
-incomplete reaction
-unwanted side reactions
-practical losses(solid may get lost when being transferred between beakers
what is the atom economy of a reaction
atom economy is a measure of the efficiency of the reaction. it looks at the amount of reactants that get turned into useful products
how can atom economy be calculated
atom economy =
(mr of desired product , total mr of reactants) x 100
fill in the gap : ‘The ___ the atom economy the more sustainable and efficient the process
higher
how can percentage error be calculated
% error =
(absolute uncertainty / calculated value) x 100
