pH Regulation

Water, , is an amphoteric substance--it can act as either an acid or a base. In certain circumstances, water can act as a Bronsted-Lowry acid by donating a proton.

As seen above, donated one of its hydrogen atoms, becoming .

In other cases, water can act as a Bronsted-Lowry base by accepting a proton.

As seen above, accepted a hydrogen atom to become .

Therefore, water can act as either an acid or a base depending on the situation. There are other amphoteric substances, but water is definitely the most common.

Here is the equation needed to find the correct answer to this question.

This question requires you to use the Henderson-Hasselbach equation, one of the most important equations in biochemistry. The equation is:

where is the concentration of the conjugate base, and is the concentration of the acid. In this scenario, is the conjugate base, while is the acid. With the numbers given in this question, the equation should look like this:

Here are the equations we need to use to find the pOH of our solution of sulfuric acid:

Normal blood pH is 7.4. A decrease in pH could indicate acidosis, which is associated with too much in the blood. Respiratory acidosis occurs as the result of the lungs failing to eliminate enough .

Buffering capacity refers to how well a buffer works. A buffer is a substance that maintains a specific pH regardless of added acid or base. Thus, buffering capacity refers to how well a buffer maintains the pH of a solution despite the the effects of added acid or base. The other choices do not apply to this definition.

The best buffering capacity occurs when pH = pKa. When this is true, the ratio of ionized to unionized form of the buffer is 1:1. Thus the solution can best resist changes in pH, as hydrogen ions can be quenched or donated to solution to resist change. Acetic acid would have almost the same buffering capacity since its pKa is almost as close to 4.0 as that of formic acid.

Using the Henderson Hasselbach equation:

Thus, the ratio of acid to base =

Recall the equation for pH. Here is the calculation that should be performed:

pH is calculated via the following equation:

refers to the concentration of hydrogen ions in the solution, which in this case is the same as the concentration of the acid since hydrochloric acid is a strong acid and will fully dissociate in solution. Thus, we have: