Assuming complete dissociation of the salts, calculate the ionic strength of

(a)0.2mMKNO3

(b)0.2mMCs2CrO4

(c) 0.2mMMgCl2plus0.3mMAlCl3

Short Answer

Expert verified

(a) The ionic strength of 0.2m MKNO is 0.2mM

(b) The ionic strength of0.2mMCs2CrO4 is 0.6mM

(c) The ionic strength of0.2mMMgCl2 plus0.3mMAlCl3 is 2.4mM

Step by step solution

01

Define the ionic strength

The ionic strength of a solution is the amount of ion concentration in it. It's written in the form of I. It has an impact on ion activity. The ion interaction with water and other ions in the solution is marked. The ionic strength formula is used to calculate half of each ionic species' total concentration.

The formula for ionic strength is as follows:

I=121nCiZj2

02

Calculate the ionic strength of KNO3

The given data is

0.2mM solution ofKNO3

Calculate the ionic strength by using the ionic strength calculation formula

μ=12K++12+NO3--12=120.2+12+0.2-12mM=120.4mM=0.2mM

The ionic strength of 0.2mM KNO is 0.2mM.

03

Calculate the ionic strength of Cs2 CrO4

The given information is

0.2mM solution ofCs2CrO4

Calculate the ionic strength by using the ionic strength calculation formula

μ=122Cs++12+CrO32--22=120.4+12+0.2-22mM=121.2mM=0.6mM

The ionic strength of 0.2mM Cs2CrO4is 0.6mM.

04

Calculate the ionic strength of 0.2m MMgCl2

The given data is

0.2mMMgCl2plus0.3mMAlCl3

Calculate the ionic strength by using the ionic strength calculation formula

μ=122Mg2++22+2Cl--12+Al3+32+3Cl--12=120.2+22+0.4-12+0.332+0.9-12mM=120.8+0.4+2.7+0.9mM=2.4mM

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Most popular questions from this chapter

Sodium acetate hydrolysis treated by Solver with activity coefficients.

(a) Following the NH3 example in Section 8-5, write the equilibria and charge and mass balances needed to find the composition of 0.01 M sodium acetate (Na+A-). Include activity coefficients where appropriate. The two reactions are hydrolysis (pKb = 9.244) and ionization of H2O.

(b) Including activity coefficients, set up a spreadsheet analogous to Figure 8-12 to find the concentrations of all species. Assign an initial value of ionic strength = 0.01. After the rest of the spreadsheet is set up, change the ionic strength from the numerical value 0.01 to the correct formula for ionic strength. This two-step process of beginning with a numerical value and then going to a formula is necessary because of circular references between ionic strength and concentrations that depend on ionic strength. There are four unknowns and two equilibria, so use Solver to find 4 - 2 = 2 concentrations (pC values). Solver does not find both pC values at the same time well in this problem. Execute one pass to find both pC values by varying pA and pOH to minimizeΣbi2 . Then vary only pA to minimizeΣbi2 . Then vary only pOH to minimize Σbi2. Continue alternating to solve for one value at a time as long as Σbi2 continues to decrease. Find [A-], [OH-], [HA], and [H+]. Find the ionic strength, pH =-log([H+] γ+) and the fraction of hydrolysis = [HA]/F.

(a) Following the example of Mg(OH)2 in Section 8-5, write the equations needed to find the solubility of Ca(OH)2. Include activity coefficients where appropriate. Look up the equilibrium constants in Appendixes F and I.

(b) Suppose that the size of CaOH+= Ca(H2O)5(OH)+ is 500 pm. Including activity coefficients, compute the concentrations of all species, the fraction of hydrolysis (= [CaOH+]/{[Ca2+] + [CaOH+]}), and the solubility of Ca(OH)2 in g/L. The Handbook of Chemistry and Physics lists the solubility of Ca(OH)2 as 1.85 g/L at 00C and 0.77 g/L at 1000C

Using activities, calculate the pH of a solution containing 0.010 M NaOH plus 0.012 0 M LiNO3 . What would be the pH if you neglected activities?

(a) Ion Pairing . As in problem 8-30, find the concentration, ionic strength, and ion pair fraction in 0.025FMgSO4

(b) Two possibly important reactions that we did not consider are acid hydrolysis of Mg+Mg2++H2O֏MgOH++H+and base hydrolysis of SO2-4. Write these two reactions and find their equilibrium constants in Appendices I and G. With the assumed pH near 7.20 and neglecting activity coefficient, show that both reactions are negligible.

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

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