PHYSICAL - AMOUNT OF SUBSTANCE

Question 1

Relative atomic mass

Answer 1

the average mass of an atom of an element relative to one twelfth of the mass of an atom of carbon-12.

Question 2

Relative molecular mass

Answer 2

Ratio of the mass of 1 molecule to 1/12 of the mass of carbon-12

Question 3

Avogadro’s constant

Answer 3

6.02x10^23

Question 4

Equation linking concentration and volume
amount

Answer 4

amount(mol/g) = conc x vol
cm3/1000 = dm3
conc = mass/volume

Question 5

Equation linking mass and Mr

Answer 5

mass = mol x Mr

Question 6

Titration calculation
0.25dm3 of a solution of CuSO4 weighs 47g. Calculate conc in mol dm-3:

Answer 6

Mr of CuSO4 = 159.6
mol = 47/159.6 = 0.294mol
0.294/0.25 = 1.18moldm-3

Question 7

Back titration
A metal carbonate, M2CO3 reacts with HCl -> M2CO3 + 2HCl –> 2 MCl + CO2 + H2O. 4.5g M2CO3 dissolved to make a 250cm3 solution - 25cm3 of this was neutralised by 28.9cm3 of 0.148moldm-3 HCl.

Answer 7

1. Calc mol of HCl in 28.9cm3 of 0.148moldm-3 HCl:
   28.9/1000 x 0.148 = 4.28x10-3 mol
2. Calc mol of M2CO3 that reacted with this HCl
   (4.28x10-3)/2 = 2.14x10-3mol
3. Calc mol of M2CO3 in the 4.5g sample
   2.14x10-3 x 10 = 0.0214mol
4. Calculate RFM of M2CO3
   Mr = mass/mol
   4.5 / 0.0214 = 150.3
   150.3+12+(16x3) = 210.3 Mr

Question 8

Ideal gas equation

Answer 8

PV = nRT
P = pressure (Pa) KPa -> Pa = x1000
V = vol (m^3) cm3 -> m3 = /1000000
n = mol
R = gas constant
T = Kelvin (K) °C -> K = +273

Question 9

Empirical formula

Answer 9

Simplest whole number ratio of atoms of each element in a compound

Question 10

Molecular formula

Answer 10

Actual number of atoms of each element in a compound

Question 11

EF calculation

Answer 11

1. Divide mass/% of element by its Ar
2. Work out simplest ratio
3. Formula

Question 12

MF calculation

Answer 12

1. Divide actual Mr of compound by Mr of EF
2. Multiply EF by answer

Question 13

Hydrated compounds

Answer 13

1. Mass/atomic mass
2. Ratio
3. Formula

Question 14

Atom economy

Answer 14

(Mr of useful product/Mr of all products) x100
Efficient processes: High AE, important for sustainable development as less waste produced and less natural resources used
Wasteful products can be sold for profit