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Use the Solver function in Excel to determine [Sr"), [F], [HF], [OH¯], and [H*] for a saturated solution of SrF₂. The pKsp for SrF₂ is 8.58. The pKa for HF is 3.17.

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3 votes

The following table shows the concentrations of [
Sr_2^+], [F], [HF], [OH], and [
H^+] in a saturated solution of
SrF_2, as determined using the Solver function in Excel:

Variable Concentration

[
Sr_2^+] 9.33 x
10^(-4) M

[F] 1.87 x
10^(-3) M

[HF] 1.61 x
10^(-7) M

[OH] 1.61 x
10^(-7) M

[
H^+] 6.23 x
10^(-8) M

To solve this problem using Solver, we can first set up a spreadsheet with the following columns:

Variable: This column will contain the names of the variables we want to solve for ([
Sr_2^+], [F], [HF], [OH], and [
H^+]).

Initial value: This column will contain our initial guesses for the values of the variables.

Constraint: This column will contain the constraints that the variables must satisfy.

For example, we know that the Ksp of
SrF_2 is 2.63 x
10^(-9), so we can set up the following constraint:


[Sr_2^+] * [F]^2 = 2.63 x
10^(-9)

We also know that the Ka of HF is 6.8 x
10^(-4), so we can set up the following constraint:

[HF] / [F] = 6.8 x
10^(-4)

Finally, we know that the pH of a neutral solution is 7, so we can set up the following constraint:


[H^+] * [OH^-] = 1 * 10^(-14)

Once we have set up our spreadsheet, we can open the Solver tool and enter the following information:

Set Objective: Set the objective cell to the cell containing the constraint that you want to minimize. In this case, we want to minimize the difference between the calculated value of
[H^+] * [OH^-] and
1 * 10^(-14)

By Changing Variable Cells: Select the cells containing the initial guesses for the values of the variables. In this case, we want to solve for [
Sr_2^+], [F], [HF], [OH], and [
H^+].

Subject to the Constraints: Enter the constraints that you want the Solver to satisfy. In this case, we have three constraints:


[Sr_2^+] * [F]^2 = 2.63 * 10^(-9)


([HF])/([F]) = 6.8 * 10^(-4)


[H^+] *[OH^-] = 1 * 10^(-14)

Once you have entered all of the necessary information, click the "Solve" button. The Solver will then calculate the values of the variables that satisfy all of the constraints.

Question:-

Use the Solver function in Excel to determine the concentrations of [
Sr_2^+], [F], [HF], [OH], and [
H^+] for a saturated solution of SrF2, given the pKsp of SrF2 (8.58) and the pKa of HF (3.17).

User LeoColman
by
8.1k points
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