Question

Worksheet 17c (Gen Chem) Other Equilibria - Calculate the free cobalt(II)ion concentration in a solution that is initially 0.010 M cobalt(II) nitrate and 1.00 M ammonia. (Hint: assume 1 L of solution). How does decreasing the pH affect the free cobalt(II) id concentration? Explain.

Answer 1

Reaction: Co(NO3)2 + 6NH3 ----> Co(NH3)6²⁺

Here, the free [Co²⁺] = 0 becasue cobalt nitrate is the limiting reagent in the above reaction.

The molar ratio Co(NO3)2:NH3 = 1:6

But here, NH3 is in large excess, so Co²⁺ or Co(NO3)2 is the limiting reagent. As a result, all the Co(NO3)2 will get consumed.

Hence, the free [Co²⁺] = 0

Decreasing the pH increases the free [Co²⁺] because as pH decreases, then [H⁺] increases.

Co(NO3)2 + 2H⁺ ----> Co²⁺ + 2HNO3