Question

For each of the following factors, indicate whether the pH increases or decreases and explain why the factor may cause variation in pH in streams or water bodies (read background pgs. 4 and 5):
a) Photosynthesis (6CO2 + 6H20 ------> C6H1206+602): pH increases / decreases EXPLAIN
b) Respiration (C6H1206+ 02 ----> CO2 + H2O + ATP): pH increases / decreases EXPLAIN:
c) Contamination with substance that releases hydroxyl/hydroxide ions: pH increases / decreases EXPLAIN:
d) Contamination with substance that releases hydrogen ions: pH increases or decreases EXPLAIN:

Answer 1

Answer:

a) Photosynthesis ( 6CO₂+ 6H₂0 ------> C₆H₁₂0₆ + 60₂): pH increases

b) Respiration ( C₆H₁₂0₆+ 0₂ ----> CO₂  + H₂O + ATP): pH decreases

c) Contamination with substance that releases hydroxyl/hydroxide ions: pH increases

d) Contamination with substance that releases hydrogen ions: pH decreases

Explanation:

(1) More the acidic environment, lesser will be the pH.

(2) More will be the basic environment, more will be the pH.

a) Photosynthesis ( 6CO₂+ 6H₂0 ------> C₆H₁₂0₆ + 60₂): pH increases:

During photosynthesis, carbon dioxide (CO₂) is utilized to produce oxygen (O₂). CO₂ is responsible for making the environment acidic because it has tendency to combine with water (H₂O) so as form form carbonic acid (H₂CO₃). The reaction is mentioned as under:  

                  CO₂ + H₂O  ⇄  H₂CO₃

But, during photosynthesis carbon is being used as a result of which it's concentration is decreasing in the environment. Less CO₂ means less acidic environment leading to an increase in pH.

b) Respiration ( C₆H₁₂0₆+ 0₂ ----> CO₂  + H₂O + ATP): pH decreases:

During respiration, carbon dioxide (CO₂) is being produced as a result of which environment will become more acidic leading to a decrease in pH.

c) Contamination with substance that releases hydroxyl/hydroxide ions: pH increases:

When hydroxyl/hydroxide ions [OH⁻] in the environment increase, it adds to the basicity and decreases acidity. An increase in basic environment leads to an increase in pH.

d) Contamination with substance that releases hydrogen ions: pH decreases:

When hydrogen ions [H⁺] in the environment increase, it adds to the acidity and decreases basicity. An increase in acidic environment leads to a decrease in pH.