2.3 Amount of Substance

Question 1

What is a mole ?

Answer 1

Amount of any substance certaining as many particles as there are carbon atoms in 12g of carbon-12.

Question 2

What is Avogadro’s constant ?

Answer 2

6.02x10^23
It is the number of atoms per mole of carbon-12.

Question 3

What is molar mass ?

Answer 3

It is the mass per mole of a substance (g/mol-1)

Question 4

How to work out number of moles?

Answer 4

Mass (g) / molar mass (g/molar-1)

Question 5

How to work out number of particles ?

Answer 5

Number of moles x Avogadro’s constant

Question 6

What does 1 mole of gas at room temperature and pressure obtain?

Answer 6

24 dm^3 (24dm^3 = 24000cm^3)

Question 7

Molecular Formulae

Answer 7

Number of atoms of each element in a molecule.

Question 8

Empirical Formula

Answer 8

Simplest whole number ratio of atoms of each element in a compound.

Question 9

How to calculate empirical formula ?

Answer 9

1) Mass/molar mass = no of moles.
2) Divide by smallest number.
3) Make a whole number ratio.
4) Create formula.

Question 10

Relative molecular mass

Answer 10

Compares mass of molecule with mass of an atom of carbon-12.

Question 11

Relative formula mass

Answer 11

Compares mass of formula unit to that of an atom of carbon-12.

Question 12

Why are many coloured salts hydrated ?

Answer 12

This is because water is a part of their crystalline structure. This water is known as the water of crystallisation.

Question 13

What happens when copper (II) sulphate salt is heated ?

Answer 13

Water bonds within the crystal are broken and water is driven off leaving behind the white anhydrous powder.

Question 14

Equation for copper (II) sulphate reaction

Answer 14

CuSO4.5H2O = CuSO4 + 5H2O

Question 15

What happens to heated CuSO4 when no water is returned ?

Answer 15

Crystalline structure is lost and white anhydrous powder remains.

Question 16

Equation for volume

Answer 16

Volume = number of moles x 24 dm^3

Question 17

What is the ideal gas equation ?

Answer 17

pV = nRT

P= pressure 1atm = 101000pa
V = volume 1dm = 1000cm
N = no of moles (mol)
R = molar gas constant =8.314 mol-1
T= temp(•c) +273 = kelvin

Question 18

What is concentration ?

Answer 18

Concentration is the number of moles of a solute dissolved in 1dm^3 of a solution.

Question 19

What is the equation for finding concentration?

Answer 19

concentration= Mass or Moles / Volume

Question 20

What is a standard solution?

Answer 20

A solution with a known concentration.

Question 21

What is the molar gas volume ?

Answer 21

Volume per mole of gas molecules at standard temperature and pressure.

Question 22

Equation for Molar gas volume

Answer 22

number of moles= volume/molar gas volume

Question 23

What is the stoichiometry ?

Answer 23

The ratio of number, from balanced equation, of the amount of moles of each substance.

Question 24

What is percentage yield ?

Answer 24

% of a desired product.

Question 25

What is theoretical yield ?

Answer 25

Maximum possible amount of product that can be produced.

Question 26

What is actual yield ?

Answer 26

How much product is actually produced from a reaction. Usually lower than theoretical yield.

Question 27

Equation for percentage yield

Answer 27

%=actual yield/theoretical yield x 100

Question 28

What are excess and limiting reagents ?

Answer 28

Limiting reagent is reactant not in excess that gets used up first in reaction.

Question 29

How to find limiting reagent ?

Answer 29

1) Find moles of each reactant in equation. 2)Find smallest amount of moles. 3)Use mole number to find amount of moles for other products based on stoichiometry.

Question 30

What is atom economy ?

Answer 30

Atom economy is a measure of how well the atoms have been utilised.

Question 31

Equation for atom economy

Answer 31

sum of desired amount/ sum of molar mass of all x 100

Question 32

Why are high atom economies good ?

Answer 32

Means reaction produced large quantities of desired product, with little waste products being made. More sustainable as it makes most use out of natural resources used.