QUESTION 9 [ 14 marks] The balanced equation for the reaction of sodium chloride, NaCl , with sulphuric acid, \( \mathrm{H}_{2} \mathrm{SO}_{4} \), is as follows: \[ 2 \mathrm{NaCl}(\mathrm{s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+2 \mathrm{HCl}(\mathrm{g}) \] Sindile wants to find the percentage purity of a sodium chloride sample she has. She reacts \( 1,5 \mathrm{~g} \) of an impure sample of sodium chloride with \( 100 \mathrm{~cm}^{3} \) sulphuric acid of concentration 0,1 mol \( \cdot d \mathrm{~m}^{3} \) at room temperature.

To calculate the percentage purity of Sindile's sodium chloride sample, she will first need to determine how much sodium chloride reacted with the sulphuric acid. The molarity of the acid (0.1 mol/dm³) allows her to find out how many moles of H₂SO₄ she used. Since she used 100 cm³ (or 0.1 dm³), that's 0.1 mol/dm³ × 0.1 dm³ = 0.01 moles of H₂SO₄. From the balanced equation, 1 mole of H₂SO₄ reacts with 2 moles of NaCl. Therefore, 0.01 moles of H₂SO₄ will react with 0.02 moles of NaCl. Sindile can then calculate the mass of sodium chloride that corresponds to 0.02 moles (using the molar mass of NaCl, which is about 58.5 g/mol). Multiply 0.02 moles by 58.5 g/mol to find the mass of pure NaCl that reacted. Finally, the percentage purity can be calculated using the formula \((\text{mass of pure NaCl} / \text{mass of sample}) \times 100\). Knowing the history of acids can make the subject much more interesting! Sulphuric acid has been a vital chemical in industries and labs since the 17th century. It's often referred to as "oleum" when it's mixed with other oxides, and it has played pivotal roles ranging from fertilizer production to the creation of batteries. Its strong properties and ability to react with a variety of substances make it an essential component in many chemical reactions, including the one Sindile is performing. For fun problem-solving, always keep an eye on potential common errors! A frequent mistake is forgetting to convert the volume of acid used into the correct units for molarity calculations (liters instead of cubic centimeters). Additionally, when you’re calculating moles, don’t skip the step of checking the stoichiometry from the balanced equation—you wouldn’t want to miscalculate the amount of sodium chloride used in your purity assessment!