For the following solutions of strong and weak bases determine the concentration

Question

For the following solutions of strong and weak bases determine the concentrations of base [B] [OH-] and the pH of the solution.
A. 2.50 g of KOH(FW=56.1g/mole) dissolved in water to make 5.00 L of solution
B. 1.500 g of sodium acetate dissolvie kn water to make 750 ml of solution For the following solutions of strong and weak bases determine the concentrations of base [B] [OH-] and the pH of the solution.
A. 2.50 g of KOH(FW=56.1g/mole) dissolved in water to make 5.00 L of solution
B. 1.500 g of sodium acetate dissolvie kn water to make 750 ml of solution
A. 2.50 g of KOH(FW=56.1g/mole) dissolved in water to make 5.00 L of solution
B. 1.500 g of sodium acetate dissolvie kn water to make 750 ml of solution

Explanation / Answer

a)

m = 2.5 g of KOH

mol = mass/MW = 2.5/56.1 = 0.0445632 mol of KOH

V = 5 L

M = mol/V = 0.0445632/5

M = 0.008912 M of KOH

pOH =-log(OH) = -log(0.008912 = 2.0500

pH = 14-2.0500 = 11.95

b)

m = 1.5 g of NaAcetate...

mol = mass/MW = 1.5/82 = 0.01829 mol of NaAc

V = 0.75

M = mol/V = 0.01829 /0.75 = 0.02438 M

A- + H2O <-> HA + OH-

Kb = [HA][OH-]/[A-]

Kb = Kw/Ka = (10^-14)/(1.8*10^-5) = 5.55*10^-10

5.55*10^-10 = x*x/(0.02438 -x)

x = H+ = 3.678*10^-6

pH= -log( 3.678*10^-6) = 5.434

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