Cobalt salt + KNO2 + CH3COOH -> yellow ppt. The yellow precipitate is: — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: When a cobalt(II) salt is treated with potassium nitrite (KNO2) in the presence of acetic acid (CH3COOH), the cobalt(II) is oxidized to cobalt(III) by nitrous acid. Step 2: The cobalt(III) then coordinates with nitrite to form the stable complex [Co(NO2)6]3-, which precipitates with potassium ions as K3[Co(NO2)6]. Step 3: The common name of this bright yellow crystalline precipitate is potassium cobaltinitrite, matching option (b).