What is Alkalinity?

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 Alkalinity is defined as the acid neutralizing capability of a system. For a system with only carbonate, the alkalinity is defined by the following equation:

In this equation all the inorganic species of carbon that can neutralize a proton are included. The factor of two for carbonate is due to its ability to consume two moles of protons for every mole of carbonate.

Using alkalinity test strips, such as those available for swimming pool or hot tub testing, test the alkalinity of the following solutions:

1. Put 125 mL (~1/2 cup) of fresh water into each of four 12-16 oz cups. Determine the pH and alkalinity of the water in cup #1.

2. Blow vigorously through a straw into the second cup for three minutes. Determine the pH and alkalinity of the solution.

3. Add 1/8 teaspoon of baking soda to the third and fourth cups. Swirl until it dissolves. Measure the pH and alkalinity of cup #3.

4. Blow vigorously through a straw into the fourth cup for three minutes. Determine the pH and alkalinity of the solution.

5. Add a few drops of vinegar to cups #1 and #3 and swirl to mix. Determine the pH in each cup.

1. How did the pH of the low alkalinity water change when you blew into it with a straw? Why did this change occur?

2. How did adding baking soda change the result? Why?

3. How much did the pH change when you added acid to:

a) Cup #1?
b) Cup #3?
c) Why the difference?

4. How might this relate to the uptake of carbon by the ocean?

1. Show that the alkalinity of a beaker of water exposed to carbon dioxide is equal to zero.

2. What is the alkalinity of a closed beaker with 0.1 M Na2CO3?

3. Borate (B(OH)4-) is a significant component of sea water. Draw the Lewis structure of borate and write an acid base reaction of borate with water. Modify the equation for alkalinity to include borate. Is it reasonable to classify B(OH)4 as a Bronsted-Lowry base?