What is the molar mass of 0.250 mol of aluminium sulfate (Al₂(SO₄)₃)? [Al = 27.0, S = 32.1, O = 16.0]

The formula $\text{Al}_2(\text{SO}_4)_3$ means there are 2 Aluminium atoms, 3 Sulfur atoms (from $3 \times \text{S}$), and 12 Oxygen atoms (from $3 \times 4 \times \text{O}$).

$$\text{Molar mass} = (2 \times \text{Al}) + (3 \times \text{S}) + (12 \times \text{O})$$ $$\text{Molar mass} = (2 \times 27.0) + (3 \times 32.1) + (12 \times 16.0)$$ $$\text{Molar mass} = 54.0 + 96.3 + 192.0$$ $$\text{Molar mass} = 342.3 \text{ g/mol}$$

The molar mass of aluminium sulfate is a constant value, regardless of the number of moles.

The molar mass of aluminium sulfate is $342.3 \text{ g/mol}$. The quantity of 0.250 mol is extra information if the question strictly asks for "molar mass". If it asked for the "mass of 0.250 mol", the calculation would be different.

The molar mass of aluminium sulfate ($\text{Al}_2(\text{SO}_4)_3$) is $\boxed{\text{342.3 g/mol}}$.

1. (b) Write the formula for each of the following ions:

(i) carbonate (IV) ion

(ii) nitrate (V) ion

(i) Carbonate (IV) ion:

$$\boxed{\text{CO}_3^{2-}}$$

(ii) Nitrate (V) ion:

$$\boxed{\text{NO}_3^-}$$

1. (c) Name the following organic compounds:

(i) $\text{CH}_3\text{CH}_2\text{CH(Br)}\text{CH}_3$

(ii) $\text{CH}_3\text{COCH}_2\text{CH}_3$

(i) $\text{CH}_3\text{CH}_2\text{CH(Br)}\text{CH}_3$:
This is a butane chain with a bromine substituent. Numbering the carbon chain from the right gives the bromine the lowest possible number (carbon 2).

$$\boxed{\text{2-bromobutane}}$$

(ii) $\text{CH}_3\text{COCH}_2\text{CH}_3$:
This is a ketone with a 4-carbon chain. The carbonyl group ($\text{C=O}$) is on the second carbon from either end.

$$\boxed{\text{Butan-2-one}}$$