The equilibrium constant for dissolution of a non ionic compound, such as diethyl ether(CH3CH2OCH2CH3) , in water can be written

ether(I)֏ether(aq)K=[etheraq]γether

At low ionic strength, role="math" localid="1654837696819" γ1 for neutral compounds. At high ionic strength, most neutral molecules can be salted out of aqueous solution. That is, when a high concentration typically (>1M)of a salt such as NaCIis added to aqueous solution, neutral molecules usually becomes less soluble. Does the activity coefficient, γether increases or decreases at high ionic strength?

Short Answer

Expert verified

Thus, the neutral compound in ether would preferentially be extracted in the ether layer and can be easily separated by salting out the layer.

Step by step solution

01

Step 1:Activity Coefficient of Ether at high NaCI concentration

At high concentrations, the activity coefficient value of ether would be very low, and the value would decrease at high ionic strength. Which makes the value of as,

K=etheraq×activitycoefficient

The value is too small to extract from the aqueous layer.

02

Neutral molecules of Ether at high NaCI concentration

As a result, the neutral compound in ether will preferentially extract in the ether layer and can be easily separated by salting out the layer.

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Most popular questions from this chapter

Calculate the activity coefficient of AI3+when role="math" localid="1654836623327" μ=0.083Mby using linear interpolation in Table 8-1 .

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

Write the equilibrium expression for Ca2++2Cl-Cacl2(aq)with activity coefficients.

Why do activity coefficients not appear in the charge andmass balance equations?

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