In the alkalinity calculation Alk = [A*B*50000]/(mL sample), what do A and B denote?

• A. A = volume of sample; B = dilution factor
• B. A = mL of acid used; B = Normality of acid
• C. A = mL of base used; B = Normality of acid
• D. A = mg CaCO3 equivalent; B = titrant molarity

Answer: (B)

Alkalinity as CaCO3 is determined by how much acid is needed to neutralize the bases in a water sample, so the key inputs are the amount of acid used and the strength of that acid. In the formula Alk = [A × B × 50,000] / (mL sample), A is the milliliters of acid used in the titration, and B is the normality of that acid. Multiplying A by B gives the number of milliequivalents of acid that reacted. The factor 50,000 converts those equivalents into mg per liter as CaCO3, taking into account that CaCO3 has an equivalent weight of 50 mg/meq and the sample volume is in milliliters (hence the extra 1000 factor when converting mL to L). Because alkalinity is all about how much acid is required to neutralize the sample, those two inputs—how much acid and how strong the acid is—are the essential pieces.