Question

question 10
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explain in detail why the ph of the pondwater is lower at night.

• relate your answer to to the process of cellular respiration
• discuss co2 levels
• describe the connection betwwen co2 levels and ph

Explanation:

During the night, plants (and other organisms) in the pond carry out cellular respiration. Cellular respiration is the process by which cells break down glucose ($C_6H_{12}O_6$) in the presence of oxygen ($O_2$) to produce carbon dioxide ($CO_2$), water ($H_2O$), and energy (in the form of ATP). The chemical equation for cellular respiration is $C_6H_{12}O_6+6O_2
ightarrow6CO_2 + 6H_2O+Energy$.

As a result of cellular respiration occurring throughout the night, the concentration of $CO_2$ in the pond water increases. Carbon dioxide dissolves in water and reacts with it to form carbonic acid ($H_2CO_3$) according to the equation $CO_2 + H_2O
ightleftharpoons H_2CO_3$. Carbonic acid is a weak acid that can dissociate to release hydrogen ions ($H^+$). The dissociation of carbonic acid is $H_2CO_3
ightleftharpoons H^++HCO_3^-$.

The pH of a solution is a measure of the hydrogen ion concentration, with the formula $pH =-\log[H^+]$. As the concentration of $H^+$ ions increases (due to the formation of carbonic acid from the increased $CO_2$ levels), the pH of the pond water decreases. So, the higher $CO_2$ levels at night (from cellular respiration) lead to more carbonic acid formation, more $H^+$ ions, and thus a lower pH.

Answer:

The pH of pond water is lower at night because during the night, cellular respiration (by plants and other organisms in the pond) occurs, increasing $CO_2$ levels. $CO_2$ dissolves in water to form carbonic acid ($H_2CO_3$), which dissociates to release $H^+$ ions. Since pH is based on $H^+$ concentration ($pH =-\log[H^+]$), the increased $H^+$ (from $CO_2$-derived carbonic acid) lowers the pH.