Index2

After determining the equivalence points, calculate the half equivalence points by taking the equivalence points dertermined and dividing it by 2.

Trial 1

Trial 2

25.19 (equivalence point)/2= 12.6 (half equivalence point)

23.25 (equivalence point)/2 = 11.63 (half equivalence point)

Then use the half equivalence points to determine the ionization constant, Ka, by using simple algebra. First, take the two coordinates nearest the half equivalence points and find the slope by looking at the graph.

Trial 1

Trial 2

(12, 4.65) ; (13, 4.72)

Formula: m = (y2 - y1) / (x2 - x1) = slope

m = (4.72 - 4.65) / (13 - 12)
m = .07

(11, 4.64) ; (12, 4.71)

Formula: m = (y2 - y1) / (x2 - x1) = slope

m = (4.71- 4.64) / (12 - 11)
m = .07

Next find an equation to determine pH values.

Trial 1

Trial 2

Formula: y - y1 = m(x - x1) ; (12, 4.65)

             y - 4.65 = .07(x - 12)
                     y = .07x - .84 + 4.65
                     y = .07x + 3.81

Formula: y - y1 = m(x - x1) ; (11, 4.64)

               y - 4.64 = .07(x - 11)
                       y = .07x - .77 + 4.64
                       y = .07x + 3.87

Calculate pH values by using respective half equivalence points.

Trial 1

Trial 2

Half equivalence point = 12.6 = x
y = pH

y = .07(12.6) + 3.81
pH = 4.69

Half equivalence point = 11.63 = x
y = pH

y = .07(11.63) + 3.87
pH = 4.68

Finally, use the pH values to determine the ionization constant, Ka.

Trial 1

Trial 2

Formula: Ka = 10^-pH

Ka = 10^-(4.69)
Ka = 2.0 x 10^-5

Formula: Ka = 10^-pH

Ka = 10^-(4.68)
Ka = 2.1 x 10^-5

Conclusion:

In the end, the average ionization constant, Ka, was 2.05 x 10^-5. Our team found that the ionization constant we came out with is closest to acetic acid. Now, we can label that solution acetic acid and can conclude the other unknown solution is hypochlorous acid.

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