Question 1

Which of the following best describes the meaning of pH in water analysis?

Accepted Answer

pH is a way of expressing the hydrogen ion activity in a solution.

Question 2

A water sample has a pH of 5. Which of the following statements is correct based on the pH scale?

Accepted Answer

The sample is acidic and has a high level of hydrogen ions.

Question 3

Which ion is neutralized first during the titration of a water sample containing both hydroxide and carbonate ions?

Accepted Answer

Hydroxide (OH^-)

Question 4

What is the significance of the phenolphthalein end point (pH 8.3) in alkalinity titration?

Accepted Answer

It marks the point where all hydroxide ions and half of the carbonate ions have been neutralized.

Question 5

A water sample is titrated with sulfuric acid to a pH of 3.7. What does this measurement represent?

Accepted Answer

Total alkalinity

Question 6

Which of the following equations correctly represents the neutralization of carbonate ions during titration?

Accepted Answer

$$\mathrm{CO_3$^{2-} + H^+ \rightarrow $$HCO_3$$^-}$$

Question 7

If a water sample has a pH of 11, which ions are most likely contributing to its alkalinity?

Accepted Answer

Hydroxide and carbonate ions

Question 8

Which of the following best describes the relationship between total alkalinity and phenolphthalein alkalinity?

Accepted Answer

Total alkalinity includes all titrant added up to the methyl orange end point, including that used to reach the phenolphthalein end point.

Question 9

A sample of water from a freshwater lake has a pH of 7.5. Which of the following statements is most accurate?

Accepted Answer

The water is slightly basic and within the typical range for inland freshwaters.

Question 10

Which of the following ions does NOT contribute to the alkalinity of natural waters?

Accepted Answer

Cl^-

Question 11

During a titration, the pH drops from 10.2 to 8.3. Which chemical species is being converted?

Accepted Answer

Carbonate ions are being converted to bicarbonate ions.

Question 12

Which of the following best explains why phenolphthalein is used as an indicator in alkalinity titrations?

Accepted Answer

It changes color at a pH where hydroxide and half of the carbonate ions are neutralized.

Question 13

A water sample contains only bicarbonate ions. What is the expected pH range of this sample?

Accepted Answer

8.3 or less

Question 14

Which of the following reactions occurs when bicarbonate ions are neutralized during titration?

Accepted Answer

$$\mathrm{$$HCO_3$$^- + H^+ \rightarrow CO_2$ + H_2O}$$

Question 15

A water sample is titrated and the phenolphthalein end point is not observed. What does this indicate about the sample?

Accepted Answer

The sample contains only bicarbonate ions.

Question 16

Which of the following best describes the chemical process occurring at the methyl orange end point during alkalinity titration?

Accepted Answer

All alkaline compounds in the sample are neutralized.

Question 17

A water sample has a high pH (above 10) and shows a phenolphthalein end point during titration. Which ions are likely present?

Accepted Answer

Hydroxide and carbonate ions

Question 18

Which of the following is the correct sequence of neutralization during a typical alkalinity titration?

Accepted Answer

Hydroxide → Carbonate → Bicarbonate

Question 19

A sample of water from a stream has a pH of 8.7. Which ions are most likely contributing to its alkalinity?

Accepted Answer

Bicarbonate and carbonate ions

Question 20

Which of the following best explains why total alkalinity is important in water treatment processes?

Accepted Answer

It indicates the buffering capacity of water against acidification.

Water Analysis: pH and Alkalinity

Study Guide - Practice Questions