ii) The chemical reaction between rock phosphate and sulphuric acid produces calcium dihydros phosphate and calcium sulphate. Write the balanced chemical equation for this reaction including states. (A)

We often represent rock phosphate by the formula Ca3(PO4)2. When it reacts with sulphuric acid (H2SO4), one of the products is calcium dihydrogen phosphate, which has the formula Ca(H2PO4)2, and the other is calcium sulphate, CaSO4. Including the physical states, one acceptable balanced equation is:   Ca3(PO4)2(s) + 2 H2SO4(aq) → Ca(H2PO4)2(s) + 2 CaSO4(s) Let's quickly check the balance: • Calcium: Left = 3 (in Ca3(PO4)2); Right = 1 (in Ca(H2PO4)2) + 2 (in 2 CaSO4) = 3. • Phosphorus: Left = 2 (in Ca3(PO4)2); Right = 2 (in Ca(H2PO4)2). • Sulphur: Left = 2 (from 2 H2SO4); Right = 2 (in 2 CaSO4). • Hydrogen: Left = 2×2 = 4 (from 2 H2SO4); Right = 4 (from Ca(H2PO4)2, which has two –H2PO4 groups). • Oxygen: Left = 8 (from Ca3(PO4)2, since each PO4 has 4 O) + 8 (from 2 H2SO4, each having 4 O) = 16; Right = 8 (from Ca(H2PO4)2, 2×4 O) + 8 (from 2 CaSO4, 2×4 O) = 16. This shows the equation is balanced. Note: In practical production of single superphosphate fertilizer, water is also involved so that hydrated products are formed. For example, it is common to see the reaction written as:   Ca3(PO4)2(s) + 2 H2SO4(l) + 4 H2O(l) → Ca(H2PO4)2·H2O(s) + 2 CaSO4·2H2O(s) However, since the question asks only for the anhydrous equation including the states as given, the first equation is acceptable.