3. A 100 mL water sample is titrated for alkalinity by using 0.02 N sulfuric acid. To reach phenolphthalein end point requires 30 mL, and an additional 7.0 mL is added for the mixed bromocresol green-methyl red color changes. What is the ion forms are in this water?
A. Hydroxide-carbonate
B. Carbonate only
C. Carbonate-bicarbonate
D. Bicarbonate only