22g of hydrated Sodium Sulphate, Na2SO4 · X H2O were heated to a constant mass of 1.42g, determine the value of X in the formula.

Mass of hydrated salt = $3.22 \text{ g}$
Mass of anhydrous salt ($\text{Na}_2\text{SO}_4$) = $1.42 \text{ g}$
Mass of water lost = Mass of hydrated salt - Mass of anhydrous salt

Molar mass of $\text{Na}_2\text{SO}_4 = (2 \times 23) + 32 + (4 \times 16) = 46 + 32 + 64 = 142 \text{ g/mol}$
Molar mass of $\text{H}_2\text{O} = (2 \times 1) + 16 = 18 \text{ g/mol}$

Moles of $\text{Na}_2\text{SO}_4 = \frac{\text{Mass}}{\text{Molar mass}} = \frac{1.42 \text{ g}}{142 \text{ g/mol}} = 0.01 \text{ mol}$
Moles of $\text{H}_2\text{O} = \frac{\text{Mass}}{\text{Molar mass}} = \frac{1.80 \text{ g}}{18 \text{ g/mol}} = 0.1 \text{ mol}$

Ratio of moles $\text{H}_2\text{O}$ : moles $\text{Na}_2\text{SO}_4$

Therefore, $\text{X} = \boxed{10}$.

30) 20 $\text{cm}^3$ of 2 M Sulphuric (IV) acid reacted completely with 3.2 g of WOH ($\text{O}=16, \text{H}=1$) Calculate the R.A.M of W in the formula WOH.

Sulphuric (IV) acid is $\text{H}_2\text{SO}_3$. Assuming WOH is a monobasic hydroxide, the reaction is:

Volume of $\text{H}_2\text{SO}_3 = 20 \text{ cm}^3 = 0.020 \text{ L}$
Molarity of $\text{H}_2\text{SO}_3 = 2 \text{ M}$

From the equation, 1 mole of $\text{H}_2\text{SO}_3$ reacts with 2 moles of WOH.

Mass of WOH = $3.2 \text{ g}$

Molar mass of OH = $16 (\text{O}) + 1 (\text{H}) = 17 \text{ g/mol}$

1) The figure below shows part of non-luminous flame.

(a) (i) Describe an experiment that would confirm that region labeled A is not suitable for heating.

• Hold a thin copper wire or a wooden splinter horizontally across the non-luminous flame, ensuring that one part of the wire/splinter is in region A (the inner blue cone) and another part is in the outer blue cone (the hottest part of the flame).
• Observe which part of the wire glows red first or which part of the splinter chars first. The part in the outer blue cone will glow red or char much faster than the part in region A, confirming that region A is cooler and thus not suitable for heating.