Chapter 3 - Amount of substance

Question 1

What is Avogadro’s constant?

Answer 1

6.02 x 10^23

Question 2

What is molar mass?

Answer 2

The mass per mole of a substance, measured in g mol^-1

Question 3

What is the equation for molar mass?

Answer 3

n (amount) = m (mass)/M (molar mass)

Question 4

What is molecular formula?

Answer 4

The number of atoms of each element in a molecule

Question 5

What is empirical formula?

Answer 5

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

Question 6

What is relative molecular mass?

Answer 6

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

Question 7

What is relative formula mass?

Answer 7

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

Question 8

What is a hydrated salt?

Answer 8

A crystalline salt molecule that is loosely attached to a certain number of water molecules

Question 9

What is water of crystallisation?

Answer 9

Water molecules that are bonded into a crystalline structure of a compound

Question 10

What happens when hydrated salts are heated?

Answer 10

The bonds holding the water within the crystal are broken and the water is driven off, leaving behind a white powder anhydrous salt.

Question 11

What is a standard solution?

Answer 11

A solution of known concentration

Question 12

What is the equation for concentration?

Answer 12

Concentration = moles/volume

Question 13

What is molar gas volume?

Answer 13

The volume per mole of gas molecules at a stated temperature and pressure

Question 14

What is the equation for moles involving the molar gas volume?

Answer 14

Amount (mol) = volume/molar gas volume

Question 15

What is the molar gas volume at RTP?

Answer 15

24dm^3

Question 16

What is the ideal gas equation?

Answer 16

pV = nRT

Question 17

What two assumptions does the ideal gas equation rely on?

Answer 17

The forces between molecules are negligible and the gas molcules have negilgible size compared to the size of their container

Question 18

What is stochiometry?

Answer 18

The relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers.

Question 19

Why is it unlikely a 100% yield is obtained?

Answer 19

Reaction may be reversible, purification of the product may result in loss of some product, initial reactants may not be pure, other side reactions may have taken place

Question 20

Why is there a need for a high % yield?

Answer 20

To increase profits (wasting as little raw material as possible, maximise amount of product made from reactants)

Question 21

What is the equation for % yield?

Answer 21

% yield = actual yield/theoretical yield x 100

Question 22

What is a limiting reagent?

Answer 22

The reactant that is used up first, which limits the amount of product that can be formed

Question 23

What is atom economy?

Answer 23

A measure of the amount of starting materials that end up as useful products

Question 24

What is the equation for atom economy?

Answer 24

Atom economy = (total Mr of desired products/ total Mr of all products) x 100