Question 32 of 43intermediate🔧 ApplyShort Answer4 marks
Write the formulae of the compounds formed from the following pairs of ions. (i) Ca²⁺ and Br⁻ (ii) Al³⁺ and CO₃²⁻ (iii) K⁺ and SO₄²⁻ (iv) NH₄⁺ and Cl⁻
(i)
Answer
CaBr₂
(ii)
Answer
Al₂(CO₃)₃
(iii)
Answer
K₂SO₄
(iv)
Answer
NH₄Cl
Explanation
To write the formula of a compound formed by ions, we use the criss-cross method. The numerical value of the charge on one ion becomes the subscript for the other ion. The charges on the ions are not indicated in the final formula, and the subscripts must be simplified to their simplest ratio if they have a common factor. For polyatomic ions like CO₃²⁻ and SO₄²⁻, brackets are used if the subscript is greater than 1.