1.2 AMOUNT OF SUBSTANCE

Question 1

AMOUNT OF SUBSTANCE

what is the equation to work out moles

Answer 1

Moles= mass/mr

n is the number of moles (mol)
m is the mass (g)
M is the molar mass (g mol-1)

Question 2

AMOUNT OF SUBSTANCE

what is the equation to work out concentration

Answer 2

C=n/V
(Concentration= Moles/ Volume)

c is the concentration (mol dm-3)
n is the number of moles in solution (mol)
V is the volume (dm3)

Question 3

AMOUNT OF SUBSTANCE

How many cm3 in 1 dm3
How many dm3 in m3

Answer 3

◦ 1 dm3 = 1000 cm3
◦ 1 m3 = 1000 dm3

Question 4

AMOUNT OF SUBSTANCE

What is the standard conditions of a reaction?

Answer 4

molar gas volume is 24 dm-3 mol-1
temperature is 298 K
pressure is 100 kPa

Question 5

AMOUNT OF SUBSTANCE

The number of moles of gas can be calculated using the
equation:

Answer 5

N= V/MOLAR GAS
(moles= volume/ molar gas)

n is the number of moles of gas (mol)
V is volume (dm-3)

Question 6

AMOUNT OF SUBSTANCE

Whats is the assumptions made in an ideal gas

Answer 6

In an ideal gas the assumptions are made that:
◦ Intermolecular forces between the gas particles are negligible
◦ The volume of the particles themselves, relative to the
volume of their container, is negligible

Question 7

AMOUNT OF SUBSTANCE

What is the ideal gas equation

Answer 7

The ideal gas equation is:

pV=nRT

p is pressure (Pa)
V is volume (m3)
n is the number of moles (mol)
R is the gas constant (8.314 JK-1)
T is temperature (K)

Question 8

AMOUNT OF SUBSTANCE

Empirical Formula definition

Answer 8

The empirical formula is the simplest whole-number ratio of
atoms of each element present in a compound.

Question 9

6.2 g of P is combined with O2 to form 14.2 g of
phosphorous oxide.

Calculate the empirical formula of the
compound.

Answer 9

• mass of O2: 14.2 g - 6.2 g = 8 g
• number of moles of each element:
  P=6.2g/31 g mol-1 =0.2 mol
  O= 8g/16 mol-1=0.5 mol
• Divide through by the smallest number of moles to get the
  whole number ratio:
  P= 0.2/0.2=1 (x2 to make next one whole num= 2)
  O=0.5/0.2=2.5 (x2 to make whole num=5)

Empirical formula: P2O5

Question 10

AMOUNT OF SUBSTANCE

Molecular Formula definition

Answer 10

The molecular formula gives the number and type of atoms of
each element in a molecule. It is made up of a whole number of
empirical units.

Question 11

AMOUNT OF SUBSTANCE

e.g.,Determine the molecular formula of a compound with
empirical formula CH2 and a relative molecular mass of 224.

Answer 11

Relative molecular mass of the empirical formula:
C H2
12 + (1 × 2) = 14

Divide the relative molecular mass by that of the empirical
formula:
224/14=16

Molecular formula:
16 ×CH2 = C16H32

Question 12

AMOUNT OF SUBSTANCE

% Atom Economy equation

Answer 12

% Atom Economy= (Molecular Mass of desired products/ sum of molecular masses of all reactants) x100

Answer 13

Maximising atom economy has important economic, ethical and
environmental advantages:
◦ More sustainable (uses fewer raw materials)
◦ Minimises chemical waste
◦ Maximises effi ciency
◦ Less money is spent on separation processes

Answer 14

The limiting reagent is the reagent not in excess. It dictates the

Answer 15

Percentage yield is a measure of the percentage of reactants
that have been converted into the desired product. It gives a
measure of the efficiency of a reaction route.

Answer 16

The percentage yield is reduced by the formation of unwanted
by-products, any reactant that remains unreacted, or product
that cannot be extracted from the reaction vessel.

Answer 17

percentage yield= (actual yield/theoretical yield) x100