Physical Unit 1.2: Amount of Substance

Question 1

what # of significant figures should answers be given in?

Answer 1

the same as the lowest # of significant figures given in the question

Question 2

define relative atomic mass

Answer 2

the average mass of atoms of an element relative to 1/12th the mass of a 12C atom

Question 3

why is a 12C atom used to work out Ar?

Answer 3

it is the universal standard mass

Question 4

define relative molecular mass

Answer 4

the average mass of a molecule relative to 1/12 the mass of a 12C atom

Question 5

what is the Avogadro constant?

Answer 5

number of particles in a mole
6.022x10^23

Question 6

what is the formula linking mass, Mr & moles?

Answer 6

moles = mass/Mr
n=m/Mr

Question 7

what is the formula linking moles, volume & concentration?

Answer 7

moles = volume x concentration
n=vc

Question 8

what is the ideal gas equation & units?

Answer 8

pV=nRT
Pa, m^3, K

Question 9

how is temperature converted from C to K?

Answer 9

C + 273 = K

Question 10

what is the empirical formula?

Answer 10

the simplest whole number ratio of atoms of each element in a compund

Question 11

what is the molecular formula?

Answer 11

the actual number of atoms of each element in a compound

Question 12

how is the empirical formula calculated?

Answer 12

1. n=m/Mr or instead of m, % abundance
2. divide by smallest moles value to get ratio

Question 13

how is molecular formula calculated?

Answer 13

1. calculate empirical formula (ef)
2. divide by Mr of ef to find how many ef are in mf

Question 14

what is percentage atom economy?

Answer 14

a measure of what proportion of the total products of a reaction are the desired product vs how much is waste = a measure of efficiency
the higher the atom economy, the less waste produced

Question 15

what is the formula for percentage atom economy?

Answer 15

Mr of desired product / total Mr of all products x 100

Question 16

what is the formula for volume of a gas from GCSE?

Answer 16

volume (dm^3) = moles x 24

Question 17

what is the formula for percentage yield?

Answer 17

mass of product obtained / maximum theoretical mass of product x 100

Question 18

why is the percentage yield not always 100%?

Answer 18

reaction may be reversible
some product might have been lost when separated from reaction mixture or leaked from apparatus
some reactants may have reacted in a competing side reaction
reaction may not have gone to completion

Question 19

how is the limiting reagent identified?

Answer 19

find moles of each reactant
look at ratio b/w the reactants in the equation

Question 20

what is a monoprotic acid?

Answer 20

look at subscript # of H atoms in a molecule of acid
acid that donates one H+ ion per molecule of acid
e.g. HCl, HNO3, CH3COOH
acid:NaOH react in a 1:1 ratio

Question 21

what is a diprotic acid?

Answer 21

2 H+ ions per unit of acid
e.g. H2SO4
acid:NaOH react in a 1:2 ratio

Question 22

what is a triprotic acid?

Answer 22

3 H+ ions per unit acid
e.g. H3PO4
acid:NaOH react in a 1:3 ratio

Question 23

what are spectator ions?

Answer 23

ions that are not involved in the reaction

Question 24

what does an ionic equation show?

Answer 24

only the species involved in the reaction

Question 25

what is the ionic equation of an acid + hydroxide reaction?

Answer 25

H+(aq) + OH-(aq) –> H2O(l)

Question 26

what is the ionic equation for an acid + carbonate reaction?

Answer 26

2H+(aq) + CO3^2-(aq) –> H2O(l) + CO2(g)

Question 27

what is the ionic equation for an acid + hydrogencarbonate reaction?

Answer 27

H+(aq) + HCO3^-(aq) –> H2O(l) + CO2(g)

Question 28

what is the ionic equation for an acid + ammonia reaction?

Answer 28

H+(aq) + NH3(aq) –> NH4^+(aq)