Which of the following pairs of cations can be separated by adding NH4Cl and NH4OH to the mixture? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: NH4Cl and NH4OH comprise the Group III analytical reagent which precipitates Fe3+, Al3+, and Cr3+ as hydroxides. Step 2: Chromium(III) (Cr3+) belongs to Group III and precipitates as green Cr(OH)3. Nickel(II) (Ni2+) belongs to Group IV and remains soluble in NH4Cl/NH4OH due to the common ion effect and ammine complex formation. Step 3: Therefore, adding NH4Cl and NH4OH selectively precipitates Cr3+ as Cr(OH)3, leaving Ni2+ in solution, which separates them. This matches option (b).