M2 Amount of Substance

Question 1

What is Avogadro’s constant

Answer 1

One mole of a substance contains 6.02 x 10 23 particles.
One mole of a substance = mr

Question 2

Define molar mass and give the unit

Answer 2

The mass per mole of a substance g/mol

Question 3

How to calculate number of moles?

Answer 3

Mass ÷ mr

Question 4

Define empirical formulae

Answer 4

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

Question 5

Define relative molecular mass (Mr)

Answer 5

Comparing the mass of a molecule with the mass of an atom of carbon-12

Question 6

Define relative formula mass

Answer 6

Comparing the mass of a formula unit with the mass of an atom of carbon-12

Question 7

Describe hydrated salts

Answer 7

• Water molecules are part of hydrated salts crystalline structure.
• When blue crystals of hydrated copper sulfate are heated, bonds holding the water within the crystal are broken and the water driven off, leaving a whole anhydrous copper sulfate.

Question 8

What assumptions have to be made to calculate the formula of a hydrated salt by reacting masses?

Answer 8

• All of the water has been removed
• No further decomposition has occurred (as many salts decompose further when heated)

Question 9

Compare dm3 and litres

Answer 9

1 dm3 = 1000cm3 = 1000ml = 1l
1 cm3 = 1 ml

Question 10

How to convert between moles and volumes

Answer 10

Moles = concentration (mol/dm3) x volume (dm3)

Question 11

How to convert grams/dm3 into moles/dm3

Answer 11

Use mass ÷ mr = number of moles

Question 12

What is standard solution?

Answer 12

A solution of a known concentration, often 1 mol/dm3
Standard solutions are prepared by dissolving an exact mass of the solute in a solvent and making the solution to an exact volume.

Question 13

Define molar has volume

Answer 13

The volume per mole of has molecules at a stated temperature and pressure, usually RTP.
At the same temperature and pressure, equal volumes of different gases contain the same number of molecules.

Question 14

What is RTP?

Answer 14

20° Celsius and 101 lapa pressure
At RTP 1 mole of gas has a volume of 24dm3

Question 15

How to convert between moles and gas volumes (RTP)

Answer 15

Moles = volume ÷ 24

Question 16

What is the ideal gas equation?

Answer 16

pV = nRT
pressure (Pa) x volume (m3) = moles x ideal gas constant (8.31) x temperature (K)

Question 17

How to convert cm3 to m3?

Answer 17

x 10 *-6

Question 18

How to convert dm3 to m3?

Answer 18

x 10 *-3

Question 19

How to convert degrees Celsius to degrees kelvin?

Answer 19

+ 273

Question 20

How to convert kPa to Pa?

Answer 20

x 10*3
x 1000

Question 21

What is percentage yield?

Answer 21

(Actual yield ÷ theoretical yield) x 100

Question 22

Why is percentage yield never 100%?

Answer 22

• Incomplete reactions
• Product loss during practical preparation/purification
• Unwanted side reactions occurring

Question 23

What is the limiting reagent?

Answer 23

The reactant that is not in excess and will be completely used up first and stop the reaction.

Question 24

What is atom economy?

Answer 24

• A measure of how well atoms have been utilised
• atom economy = (mr of desired products ÷ mr of all products) x 100

Question 25

Why is a high atom economy important?

Answer 25

• Reactions produce a high proportion of desired products and few unwanted waste products
• High atom economy is important for sustainability as they make best use of natural resources

Question 26

What is the ratio of moles in an equation

Answer 26

The stoichiometry of the reaction