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# Analytical Chemistry Questions: Ionic Strength

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1. A and B react as follows: A + B = C + D. The equilibrium constant is 2.0 x 10^3. If 0.30 mol of A and 0.80 mol of B are mixed in 1 L, what are the concentrations fo A, B, C, and D after reaction?

4. The dissociation constant for hydrocyanic acid, HCN, is 7.2 x 10^-10. Calculate the percent dissociation of a 1.0 x 10^-3 M solution.

7. Fe^2+ and Cr2O7^2- react as follows: 6Fe^2+ + Cr2O2^2- + 14H+ <--> 6Fe^3+ + 2Cr^3t + 7H20. The equilibrium constant for the reaction is 1 x 10^57. Calculate the equilibrium concentrations of the iron and chromium species if 10mL each of 0.02 M K2Cr2O7 in 1.14 M HCl ad 0.12 M FeSO4 in 1.14 M HCL are reacted.

8. Write charge balance expressions for (a) a saturated solution of Bi2S3; (b) a solution of Na2S.

11. Write equations of mass balance for an aqueos saturated solution of BaF2 containing the species F-, HF, HF2-, and Ba^2+.

13. Calculate the pH of a 0.100 M solution of acetic acid using the charge/mass balance approach.

Ionic Strength

14. Calculate the ionic strengths of the following solutions: (a) 0.30 M NaCl; (b) 0.30 M Na2SO4; (c) 0.30 M NaCl and 0.20 M K2SO4; (d) 0.20 M Al2(SO4)3 and 0.10 M Na2SO4.

16. Calculate the activity coefficients of the sodium and chloride ions for a 0.00100 M solution of NaCl.

21. Calculate the pH of a solution of 5.0 x 10^-3 M benzoic acid (a) in water and (b) in the presence of 0.05 M K2SO4.

https://brainmass.com/chemistry/physical-chemistry/analytical-chemistry-questions-ionic-strength-99743

#### Solution Preview

1. A and B react as follows: A + B = C + D. The equilibrium constant is 2.0 x 10^3. If 0.30 mol of A and 0.80 mol of B are mixed in 1 L, what are the concentrations for A, B, C, and D after reaction?

4. The dissociation constant for hydrocyanic acid, HCN, is 7.2 x 10^-10. Calculate the percent dissociation of a 1.0 x 10^-3 M solution.

7. Fe^2+ ...

#### Solution Summary

This Solution contains over 200 words and calculations to aid you in understanding the Solution to these questions.

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## Ionic Activities

Find the activity(not the activity coefficient) of the (C3H7)4N+ (tetrapropylammonium) ion in a solution containing 0.005 M (C3H7)4N+Br- plus 0.005 M (CH3)4N+Cl-.

Activity coefficients :

Ionic strength .001 .005 .01 .05 0.1
(C3H7)4N+ : .966 .931 .912 .85 .82
CH3)4N+: .964 .928 .902 .82 .775

The ionic strength is equal to 1/2 the summation of the <multiple> (concentration of the species multiplied by its charge squared)
Ex: Ionic strength of .02 KBr
= 1/2 ([K](1^2)+[Br](1^2))
=1/2((.02*1) +(.02*1))
=.02

Activity=concentration*activity coefficient

The question here is, how do i figure out the concentration of the tetrapropylammonium ion for the concentration in the equation, and how do i figure out the activity coefficient? The ionic strength will be affected by mixing it in a different solution, and also, the solution has another ion with a different activity coefficient.

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