Using activities, calculate the pH and concentration of H+in 0.050MLiBr at25°C.

Short Answer

Expert verified

The pH of the given solution is 6.99

Step by step solution

01

Define the formula for PH calculation.

The pH of a solution can be calculated as,

pH=-logAH+=-log[H+]γH+

where,

AH+ - activity of hydrogne ion

γH+ - activity coefficient of hydrogne ion.

02

Calculate the PH form the activity.

Given

0.050MLiBr at 25°C

At an ionic strength role="math" localid="1654765585845" μof andγOH=0.81.

role="math" localid="1654765776290" H+γH+OH-γOH=x0.86x0.81=1.0×10-14x=1.2×10-7M.

The concentration of H+ion is1.2×10-7M

Calculate the pH by using the concentration of H+ion

pH=-log1.2×10-70.86=6.99

Thus, theof the given solution is 6.99 .

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Most popular questions from this chapter

Systematic treatment of equilibrium for ion pairing. Let’s derive the fraction of ion pairing for the salt in Box 8-1, which are 0.025FNaCI,Na2SO4,MgCI2,MgSO4. Each case is somewhat different. All of the solutions will be near neutral pH because hydrolysis reactions of Mg2+,SO2-4,Na+,CI-have small equilibrium constants. Therefore, we assume that H+=OH-and omit these species from the calculations. We work MgCI2as an example and then you asked to work each of the others. The ion-pair equilibrium constant, Kipcomes from Appendix J.

Pertinent reaction:

Mg2+CI-֏MgCI+aqKip=MgCI+aqγMgCI+Mg2+γMg2+CI-γCI-logKip=0.6.pKip=-0.6A

Charge balance (omitting H+,OH-whose concentrations are both small in comparison with Mg+,MgCI+,CI-:

role="math" localid="1655088043259" 2Mg2-+MgCI+=CI-B

Mass balance:

Mg2-+MgCI+=F=0.025MCCI-+MgCI+=2F=0.050MD

Only two of the three equations (B),(C) and (D) are independent. If you double (c) and subtract (D) , you will produce (B). we choose (C) and (D) as independent equations.

Equilibrium constant expression : Equation (A)

Count : 3 equations (A,C,D) and 3 unknowns Mg2+,MgCI+,CI-

Solve: We will use Solver to find

numberofunknowns-numberofequiliberia=3-1=2unknown concentrations.

The spreadsheet shows the work. Formal concentration F=0.0025Mappears in cell G2. We estimate pMg2+,pCI-in cell B8and B9. The ionic strength in cell B5is given by the formula in cell H24. Excel must be set to allow for circular definitions as described on page role="math" localid="1655088766279" 179. The sizes of role="math" localid="1655088853561" Mg2+,CI-are from Table 8-1and the size of MgCI+is a guess. Activity coefficient are computed in columns E,F. Mass balance b1=F-Mg2+-MGCI+,b2=2F-CI--MgCI+appears in cell H14,H15, and the sum of squares b21+b22 appears in cell H16. The charge balance is not used because it is not independentof the two mass balances.

Solver is invoked to minimizes b21+b22in cell H16be varying pMg2+,pCI-in cells B8and B9. From the optimized concentration, the ion-pair fraction =MgCI+F=0.0815is computed in cell D15.

The problem: Create a spreadsheet like the one for MgCI+to find the concentration, ionic strength, and ion pair fraction in 0.025MNaCI. The ion pair formation constant from Appendix J is log Kip=10-0.5for the reaction Na++CI-֏NaCIaq. The two mass balances are Na++NaCIaq=F,Na+=CI-Estimate pNa+,pCI- for input and then minimizes the sum of square of the two mass balances.

Interpolate in Table 8-1 to find the activity coefficient of H+when μ=0.030M

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