3 A surface water has pH 72 What type of alkalinity should w

3. A surface water has pH 7.2. What type of alkalinity should we expect in this water? If pH 9.0, what type of alkalinity should we expect?

Solution

From pH 14 to 10.2 there will be only hydroxide and carbonate alkalinity. When pH reaches 10.2 and below all hydroxide disappear.

From 10.2 to 8.3: No hydroxide alkalinity exist. Carbonate starts conversion to bicarbonate. Hence both carbonate and bi carbonates exist. But by the end of pH 8.3 all the caronate will be completely gets converted to bicarbonate. Hence no carbonate and no hydroxide below pH 8.3.

pH 8.3 to 4.3: only bicarbonate ion exists.

Answer:

Water having pH 7.2 will have only bicarbonate alkalinity.

Water having pH 9 will have both carbonate and bicarbonate alkalinity.