# Changing the pH of a Swimming Pool.

• Gaunt101
In summary, the conversation discusses the process of lowering the pH of a swimming pool with 95000L of water and a pH of 8.9 using an acidic substance. The ideal pH range is between 7.2-7.6, and trichlorocyanuric acid (TCA) is chosen as the substance to lower the pH. However, the conversation also mentions a lack of knowledge about the calculations involved due to the inability to find a Ka value for TCA. The conversation goes on to discuss using sodium carbonate as an alternative substance and the limitations of determining the necessary amount to add without knowing the alkalinity or buffer capacity of the solution.
Gaunt101

## Homework Statement

A swimming pool with 95000L of water with a pH of 8.9 needs to be lowered to a more suitable pH using an acidic substance. An ideal pH would be within the range of 7.2-7.6, so let's just assume that the pH we're hoping to achieve is 7.4. My brother chose trichlorocyanuric acid (TCA) as his substance to lower the pH, although I"m not entirely sure of the calculations involved since I've been unable to find a Ka value for TCA.

## Homework Equations

pH = -pKa + log([A-]/[HA-])
c = n/v
n = m/M
Ka = [A-][H+]/[HA-]

## The Attempt at a Solution

I assumed you would just use the first equation? I'm not entirely sure to be honest, the only way I can imagine doing this question is by assuming the Ka value of cyanuric acid and as a result you can the rearrange the first equation and solve for the concentrations of each species. Although I'm almost certain that this approach is incorrect. I'm terribly sorry I'm not particularly sure where to start.

Substance you add is only part of the problem. Not knowing what makes your pool water pH to be 8.9 you can't solve the question.

we goldfish consider changing the ph of swimming water to be a form of terrorism

Thanks for responding Borek and Tiny Tim!

I believe my brother was allowed to choose and he has chosen sodium carbonate Na2CO3. How should I start considering this problem? Would it just be trichlorocyanuric acid + Na2CO3 <--> ? and then find a Ka value of cyanuric acid?

Sorry for not being able to have a more directed question :(.

You don't know enough to solve the question, period. The only way to determine amount of whatever substance that needs to be added is an experiment.

Theoretically could you solve the question if you knew the measurements of how much sodium bicarbonate had fallen in right? I'm guessing since this is an assignment I can probably just model a realistic scenario and apply suitable values? Is there a way to solve the question if you knew the measurements? If not... then how what would you need to know, to solve the question, if I can just understand the process that'd be awesome ^_^.

Thank you so much for your time!

Gaunt.

You need to know alkalinity of the solution, or its buffer capacity. These are ways of expressing how much acid (or base) needs to be added to change pH of the solution. Assuming carbonate is the only source of pH you in theory estimate amount of acid that has to be added, but accuracy would be so low calculations are a waste of time.

## 1. How often should the pH of a swimming pool be checked?

The pH of a swimming pool should be checked at least twice a week, but it is recommended to check it daily if the pool is heavily used or if there has been heavy rainfall.

## 2. What is the ideal pH range for a swimming pool?

The ideal pH range for a swimming pool is between 7.2 and 7.8. This range is considered safe and comfortable for swimmers, and it also helps to prevent damage to the pool and equipment.

## 3. What happens if the pH of a swimming pool is too high?

If the pH of a swimming pool is too high, it can lead to cloudy or murky water, skin and eye irritation for swimmers, and it can also cause damage to the pool equipment. It can also reduce the effectiveness of chlorine, leading to potential bacterial growth.

## 4. How can the pH of a swimming pool be lowered?

The pH of a swimming pool can be lowered by adding an acidic substance, such as muriatic acid or sodium bisulfate, to the water. It is important to follow the manufacturer's instructions and test the water frequently when making adjustments.

## 5. Can the pH of a swimming pool affect the effectiveness of chlorine?

Yes, the pH of a swimming pool can greatly affect the effectiveness of chlorine. If the pH is too high, the chlorine becomes less effective in sanitizing the water. If the pH is too low, the chlorine can dissipate quickly and also cause skin and eye irritation for swimmers.

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