Which of the following pairs of cations cannot be separated by using dilute HCl? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Identify the colors of each complex: Ni(dmg)2 is cherry-red, Cu2[Fe(CN)6] is chocolate brown, and Fe(SCN)3 is blood red. Step 2: Cobalt tetrathiocyanatomercurate(II), Co[Hg(SCN)4], is a well-known coordination compound used in analytical chemistry to detect cobalt. Step 3: This complex precipitates as a deep blue crystalline solid. Hence, the correct option is (a).