2.1.3: Amount of substance

Question 1

Avogadro constant (definition)

Answer 1

Number of particles per mole

Question 2

Molar mass (definition)

Answer 2

Mass per mole (g mol-1)

Question 3

Empirical formula (definition)

Answer 3

the simplest whole number ratio of atoms of each element present in a compound.

Question 4

Molecular formula (definition)

Answer 4

the number and type of atoms of each element in a molecule.

Question 5

Empirical formula method

Answer 5

1) Ratio by mass
2) Ratio by moles
3) Divide by the smallest number of moles

Question 6

Formula for moles of a solid

Answer 6

No. moles = mass / Mr

Question 7

Formula for moles of a liquid

Answer 7

No. moles = conc. (moldm⁻³) x volume (dm³)

Question 8

Formula for moles of a gas

Answer 8

No. moles = vol (dm³) /24

or

No. moles = vol (cm³) / 24,000

Question 9

Molecular formula from empirical

Answer 9

1) Empirical formula mass
⟶ (Subscript x Aᵣ) + (subscript x Aᵣ)

2) Molar mass/EFM = Multiplier
3) Multiplier x subscript of old = subscript of new

Question 10

Atom economy

Answer 10

Mr of desired products / Mr of all products x 100

Question 11

Percentage yield

Answer 11

Actual yield / theoretical yield x 100

Question 12

Which is better, a high/low atom economy?

Answer 12

High atom economy: large proportion of desire products, few unwanted (waste) products.

Question 13

How far does atom economy determine sustainability?

Answer 13

• High atom economy is good as few waste products (consider what the waste products are)
• However percentage yield also affects sustainability, as does availability of starting materials