Chapter 3 - Amount Of Substance

Question 1

What is Avogadro’s Constant?

Answer 1

The number of atoms per mole of the carbon-12 isotope.

Question 2

What is a mole?

Answer 2

The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope.

Question 3

What is the equation for the number of moles of a substance?

Answer 3

n=m/Mr
n - number of moles (mol)
m - mass (g)
Mr - molar mass (g/mol)

Question 4

What is the molecular formula?

Answer 4

The number of atoms of each element in a molecule.

Question 5

What is the empirical formula?

Answer 5

The simplest whole-number ratio of atoms of each element in a compound.

Question 6

In hydrated salts, what is the name given to water molecules?

Answer 6

Waters of crystallisation

Question 7

What is the concentration of a solute?

Answer 7

The amount of solute (in moles) dissolved in each 1dm^3 of solution

Question 8

What is the equation for finding a solution’s concentration?

Answer 8

c=n/v
c - concentration (mol/dm^3)
n - number of moles (mol)
v - volume (dm^3)

Question 9

What is molar volume?

Answer 9

The volume per mole of a gas.

Measured in dm^3/mol

Question 10

What is the value of molar volume at room temperature and pressure?

Answer 10

24 dm^3/mol

Question 11

What is the equation for molar volume?

Answer 11

mgv=V/n
mgv - molar gas volume (dm^3/mol)
n - number of moles (mol)
V - volume (dm^3)

Question 12

What are the assumptions made about an ideal gas?

Answer 12

Random motion
Elastic collisions
Negligible size
No intermolecular forces

Question 13

What is the equation for the ideal gas law?

Answer 13

pV=nRT
p - pressure (Pa) 
V - volume (m^3) 
n - number of moles (mol) 
R - ideal gas constant (J/mol/K) 
T - temperature (K)

Question 14

What are the standard conditions?

Answer 14

298K and 100 kPa (1 atm)

Question 15

What is stoichiometry?

Answer 15

The balancing numbers giving the ratio of the amount, in moles, of each substance in a balanced equation.

Question 16

What are the balanced equations used to find?

Answer 16

The quantities of reactants required to prepare a required quantity of a product.
The quantities of products that should be formed from certain quantities of reactants.

Question 17

What is the percentage yield?

Answer 17

The actual yield divided by the theoretical yield expressed as a percentage.

Question 18

Why is the theoretical yield so hard to achieve? 4 reasons

Answer 18

• The reaction is incomplete.
• Competing side reactions giving different products.
• Loss of product in handling and purification.
• Reversible reaction.

Question 19

What is the limiting reagent?

Answer 19

The reactant that is not in excess.

Question 20

What is atom economy?

Answer 20

The molar mass of desired products divided by the sum of the molar masses of all products expressed as a percentage.

Question 21

What are the benefits of a high atom economy?

Answer 21

• Produce a larger proportion of desired products>Indudtrial processeses more efficent
• Few waste products>reduces waste
• Important for sustainability, the best use of natural resources>preserves raw material

Question 22

RTP is about:

Answer 22

298K

Question 23

Conversions to remember

Answer 23

cm^3 to m^3= x10^-6
dm^3 to m^3= x10^-3
1dm^3=1000cm^3=1000ml=1 litre 
C* to K= +273
kPa to Pa= x10^3

Question 24

What is a standard solution?

Answer 24

It is a solution of known concentration

Question 25

Efficiency depends on:

Answer 25

The atom economy and the percentage yield

Question 26

How many atoms are there in 11g of propane, C3H8

Answer 26

This is a sneaky question, because it isn’t asking about propane molecules, C3H8, but the total number of atoms. You must read the question very carefully in this sort of problem.

1 mol of propane, C3H8, weighs 44g and contains 6.02 x 10 ^ 23 propane molecules = 1.5 x 10^23

Each propane molecule contains 11 atoms (3 carbons and 8 hydrogen).

Therefore the total number of atoms = 11 x 1.5 x 10 ^23
= 1.65 x 10^24