The anthocyanin in hydrangeas can be isolated and used as an environmentally fri

Question

The anthocyanin in hydrangeas can be isolated and used as an environmentally friendly p^H indicator for titrations. At the end of a titration reaction of a strong acid with a strong base, you have a neutral solution. What color do you expect anthocyanin to be at the end of a titration? Describe a lab experiment to support your prediction. To increase the acidity of soil, you can add peat, which contains a complex acid mixture known as humic acid, The complexity of the humic acid it difficult to determine how acidic you are making the soil. You decide to use a titration to get a better measure. If titration of 50.0 mL extraction from the peat requires 7.0 mL of 1.0mH sodium hydroxide, what is the concentration of humic acid in the peat?

Explanation / Answer

Ans 3

At the end of a titration reaction of a strong acid with a strong base, we have a neutral solution. At the end of a titration the color of anthocyanin will be purple.

Describe a lab experiment to support your prediction-

Titrations of 0.1M NaOH and 0.1M H2SO4 (strong acid-strong base titration),using Anthocyanins as a natural pH indicator.

A strong acid and strong base both ionizes completely in solution. Therefore, when a strong acid is combined with a strong base it produces a salt

H2SO4 (aq) +2 NaOH (aq) --------à Na2SO4 +2H2O (l)

Since the Na2SO4 produced has no effect upon pH, when an equivalent amount of NaO H is added to a solution of H2SO4 the solution has a neutral pH (i.e. pH = 7.0)

This anthocyanin will be red at low pH value. It will be purple in neutral solution. It will be greenish-yellow if the solution is basic. We have to titrate until the color of the solution is purple.

Ans 4

mmol of base used =MV = (7*10^-3)(10*10^-9) = 7*10^-11 mol
so
for 2 mol of base = 1 mol of acid

7*10^-11 mol of base = (7*10^-11)/2 = 3.5*10^-11 mol of acid present

[Acid] = mol/V =(3.5*10^-11)/(50) = 7*10^-13 mol per liter

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