Question

1. a. Define alkalinity of a water sample. b. What is/are the principle ions contributing to the alkalinity of a water sample? 2· "P" and "T"alkalinities are determined for a water sample in this experiment. a. Differentiate between the Experimental Procedures of the two determinations. b. What is the color change at the "P" endpoint? What is the color change at the T" endpoint? c. Explain why the "T" alkalinity is generally greater than the "P alkalinity for a water sample. d. Suppose hydroxide ion, OH, is the only anion contributing to the alkalinity of the sample. How will the "P" and "T. alkalinity values compare? 3. The "P" alkalinity represents a value at which the bases dissolved in the water sample have been mono-protonated, while T" alkalinity represents a value at which all bases have been fully protonated by the strong acid in the titration. what is the chemical formula of the following at the "P" and "T. endpoints? "P" endpoint " endpoint a. CO, b. OH c. PO d. Sio,2

Answer 1

1. a) Alkalinity of a water sample is a measure of its ability to neutralize acids because of presence of dissolved alkaline salts (salts of weak acid and strong base). It also indicates its ability to resist a change in its pH on addition of an acid/base (i.e. its buffer capacity) because the salts donate or absorb a proton (H⁺) as needed in a particular situation.

b) The principal ions contributing to the alkalinity of a water sample are bicarbonate (HCO₃^-), carbonate (CO₃^2-) and hydroxide (OH^-). There may be other ions like phosphate, borate, silicates etc. that contribute to the alkalinity of a water sample but their contribution is very less.