Chapter 3 (2.1.3)

Question 1

What is ‘amount of substance’?

Answer 1

A quantity, n, to count the number of particles in a substance, measure in moles, mol.

Question 2

What is a mole?

Answer 2

1 mole is the amount of substance that contains 6.02x10^23 particles = Avogadro constant, Na

Question 3

What is the Avogadro constant?

Answer 3

Na is the number of particles in each mole of carbon-12.

Question 4

What is molar mass and the formula that links it with moles?

Answer 4

Molar mass is the mass in grams in each mole of the substance - g/mol
moles = mass/molar mass

Question 5

What is relative molecular mass?

Answer 5

Relative molecular mass, Mr, compares the mass of a molecule with the mass of an atom of carbon-12.
- (calculate by adding up Ar values for atoms in molecule)

Question 6

What is relative formula mass?

Answer 6

Relative formula mass compares the mass of a formula unit with the mass of an atom of carbon-12
- (calculate by adding up Ar values of elements in empirical formula)

Question 7

What is analysis?

Answer 7

• investigating the chemical composition of a substance

- formula can be calculated from results of experiments

Question 8

Define hydrous/hydrated

Answer 8

Water molecules are part of their crystalline structures (many coloured crystals are hydrated)

Question 9

Define anhydrous

Answer 9

Containing no water molecules in its crystalline structure

Question 10

Define water of crystallisation

Answer 10

The water molecules that are bonded into a crystalline structure of a compound (shown as a large dot ·)

Question 11

What happens when e.g. hydrated copper (II) sulfate crystals are heated?

Answer 11

• when blue hydrated copper sulfate crystals are heated, bonds holding the water within the crystal are broken and the water is driven off, leaving behind white anhydrous copper (II) sulfate.

Question 12

Volume conversions

Answer 12

1cm^3 = 1 ml
1dm^3 = 1l
1 dm^3 = 1000cm^3
1l = 1000ml

Question 13

What is concentration and its formula?

Answer 13

Concentration of a solution is the amount of solute (mol) dissolved in each 1dm^3 of solution (1mol/dm3)
n=cv
amount = concentration x volume

Question 14

What happens to a gas at the same temperature and pressure?

Answer 14

At the same temperature and pressure, equal volumes of different gases contain the same number of molecules.

Question 15

What is RTP?

Answer 15

RTP = room temperature and pressure

20°C and 101kPa (1 atm) pressure

Question 16

What is the molar gas volume?

Answer 16

The molar gas volume, Vm, is the volume per mole of gas molecules at a stated temperature and pressure.
At RTP, the molar gas volume = 24.0dm3mol-1

Question 17

Formula for gas moles are RTP

Answer 17

amount (mol) = volume (dm3) / molar gas volume (dm3mol-3)

n = V/24

Question 18

What is the ideal gas equation?

Answer 18

pV = nRT
pressure - Pa
volume - m^3
amount - mol
ideal gas constant - 8.314 Jmol-1K-1
temperature - K

Question 19

convert cm3 to m3 and °C to K

Answer 19

°C +273 = K

cm3 / 10^6 = m3

Question 20

What assumptions for molecules making up an ideal gas are made?

Answer 20

• random motion
• elastic collisions
• negligible size
• no intermolecular forces

Question 21

What is stoichiometry and what is it used for?

Answer 21

• stoichiometry = ratio of the amount in moles of each substance in a chemical equation
• used to find quantities of reactants and products

Question 22

What is theoretical yield?

Answer 22

The maximum possible amount of product that can be made

Question 23

Why is theoretical yield difficult to achieve?

Answer 23

• reaction may not go to completion
• other (side) reactions may have taken place unexpectedly alongside the main reaction
• purification of the product may result in some loss of the product

Question 24

What is percentage yield and its formula?

Answer 24

• percentage yield expressed the conversion of starting materials into a product
• PY = actual yield / theoretical yield X 100

Question 25

What is the limiting reagent?

Answer 25

• the reactant not in excess, which will be completely used up first and stop the reaction
• calculations must be based on limiting reagents

Question 26

What is atom economy?

Answer 26

A measure of how well atoms have been utilised in a chemical equation. Based solely on a balanced equation for a reaction and assumes 100% yield.

Question 27

Formula for atom economy

Answer 27

AE = sum of Mr of desired product / sum of Mr of all products X 100

Question 28

What are the benefits for sustainability of developing chemical processes with high atom economies?

Answer 28

• high atom economies = a large proportion of desired products and few unwanted waste products = sustainable with the best use of natural resources
• preserves raw materials and reduces waste = more efficient
• good for environmental concerns about processing or disposing of harmful waste, and dwindling finite resources.