A solution of Na_2 C0_3 is added drop wise to a solution that contains 1.01 time

Question

A solution of Na_2 C0_3 is added drop wise to a solution that contains 1.01 times 10^-2M Fe^2+ and 1.52 times 10^2 M Cd^2+. What concentration of CO_3^2 is need t initiate precipitation? Neglect any volume changes during the addition. Express your answer with the appropriate units. Significant Figures Feedback: Your answer 1.2 middot 10^12 M was either rounded differently or used a different number of significant figures than required for this part. In the solution from Part A, what will the concentration of CO_3^2- be at the moment before Fe^2+ begins to precipitate? Express your answer with the appropriate units.

Explanation / Answer

Solution :-

The concentration of the CO3^2- in the part A is 1.18*10^-12 M which will start precipating the Cd^2+ ions

For the part B The concentration of the CO3^2- before starting the precipitation of the Fe^2+ is calculated as follows

Ksp of the FeCO3 = 2.1*10^-11

FeCO3 -------- > Fe^2+ + CO3^2-

                       0.0101        x

ksp = [Fe^2+][CO3^2-]

2.1*10^-11 = [0.0101] [x]

2.1*10^-11 / 0.0101 = x

2.08*10^-9 = x

So the concentration of the [ CO3^2- ] is 2.08*10^-9 M

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