Question

question: The formation constant for CaY2 is 5.0 x 1010. At a pH 10, P4 is calculated to be 0.35 to give a conditional constant of 1.8 x 1010 Calculate pCa in 100ml of a solution of 0.100M Ca2+ at pH 10 after addition of 100ml of 0.100M EDTA​

Answer 1

1.18

Step-by-step explanation:

To calculate pCa in the given solution, we need to consider the reaction between Ca2+ and EDTA and apply the conditional formation constant.

The reaction between Ca2+ and EDTA can be represented as follows:

Ca2+ + EDTA ↔ CaY2

Given:

Formation constant (Kf) for CaY2 = 5.0 x 10^10

Conditional constant (Kc) = 1.8 x 10^10

Let's assume that x moles of Ca2+ reacts with EDTA.

At equilibrium, the concentration of Ca2+ will be decreased by x moles, and the concentration of CaY2 will be increased by x moles.

The concentration of Ca2+ at equilibrium will be (0.100 - x) M in a total volume of 200 mL (100 mL Ca2+ solution + 100 mL EDTA solution).

The concentration of CaY2 at equilibrium will be x M.

According to the formation constant equation:

Kf = [CaY2] / ([Ca2+] * [EDTA])

Using the given values, we can write the equation as:

5.0 x 10^10 = x / ((0.100 - x) * 0.100)

Now, we can solve this equation to find the value of x:

5.0 x 10^10 = x / (0.010 - 0.100x)

Cross-multiplying:

5.0 x 10^10 * (0.010 - 0.100x) = x

Expanding:

0.050 x 10^10 - 0.500 x 10^10 x = x

Rearranging and combining like terms:

1.500 x 10^10 x = 0.050 x 10^10

Simplifying:

x = (0.050 x 10^10) / (1.500 x 10^10)

x ≈ 0.03333

Now, we can calculate the concentration of Ca2+ at equilibrium:

[Ca2+] = 0.100 - x

[Ca2+] = 0.100 - 0.03333

[Ca2+] = 0.06667 M

Finally, we can calculate pCa using the concentration of Ca2+ at equilibrium:

pCa = -log10([Ca2+])

pCa = -log10(0.06667)

pCa ≈ 1.18

Therefore, the pCa in 100 mL of a solution of 0.100 M Ca2+ at pH 10, after the addition of 100 mL of 0.100 M EDTA, is approximately 1.18.