2.3 AMOUNT OF SUBSTANCE

Question 1

What is carbon-12?

Answer 1

Carbon-12 is the standard isotope used to base all atomic masses on

Question 2

What is Avogadro’s constant?

Answer 2

Avogadro’s constant is the number of particles per mole of substance.
6.02x10^26

Question 3

What is amount of substance?

Answer 3

Amount of substance is a quantity used to count the number of particles in a substance, measured in moles

Question 4

What is molar mass?

Answer 4

Molar mass is the mass of 1 mol of substance measured in g/mol

Question 5

What is the equation linking moles, mass and molar mass?

Answer 5

Amount of substance (mol) = mass (g) / molar mass (g)

Question 6

What is the molecular formula?

Answer 6

The molecular formula is the number of atoms of each element in a molecule
- O2, CO2, P4

Question 7

What is the empirical formula?

Answer 7

The empirical formula is the simplest whole number ratio of atoms or ions of each element in a compound
- Mg, C, NaCl

Question 8

What is relative molecular mass?

Answer 8

Relative molecular mass compares the mass of a molecule with the mass of an atom of carbon-12

Question 9

What is relative formula mass?

Answer 9

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

Question 10

What is water of crystallisation?

Answer 10

Water of crystallisation is water molecules that are bonded into a crystalline structure of a compound

Question 11

What are hydrous and anhydrous?

Answer 11

Hydrous- contains water molecules
Anhydrous- does not contain water molecules

Question 12

What equation links moles, concentration and volume?

Answer 12

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

Question 13

What does Avogadro’s law state?

Answer 13

Avogradro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles

Question 14

What equation links moles, volume and molar gas volume?

Answer 14

Moles (mol) = volume (dm3) / molar gas volume (24dm3/mol)

Question 15

What is the ideal gas equation?

Answer 15

The ideal gas equation is:
pressure (Pa) x volume (dm3) = moles (mol) x gas constant (8.31 J/mol/K) x temperature (K)

Question 16

What does it mean to behave like an ideal gas?

Answer 16

To be an ideal gas, gases must:
- have no forces between particles
- have a negligible size of particles

Question 17

Why do we not get 100% product yield?

Answer 17

Why we don’t get 100% product yield:
- reaction may not go to completion
- other reactions may have taken place
- purification may result in loss of product

Question 18

What is the equation for percentage yield?

Answer 18

Percentage yield = actual yield / theoretical yield x 100

Question 19

What is the limiting reagent and reagent in excess?

Answer 19

Limiting reagent and reagent in excess:
- one reactant is usually in excess (more of it than needed)
- limiting reactant will be used up and once done the reaction will stop
- limiting reactant determines how much product will form

Question 20

What is atom economy?

Answer 20

Atom economy measures how well atoms of the reactants have been put to use
- assumes 100% yield
- products of which are not desired and have to be disposed of are called waste products
- products which are not desired but can be sold or utilised elsewhere are called by-products

Question 21

What is the equation for atom economy?

Answer 21

Atom economy = molar mass(es) of desired product(s) / molar masses of all products

Question 22

Why should atom economy be improved?

Answer 22

Atom economy should be improved because:
- improves efficiency of process
- reduces waste
- preserves raw materials
- increases sustainability (meeting the needs of today without compromising the ability for future generations to meet their needs)