Question

Increasing the volume of an acid solution the pH of the solution the pKa of the acid.

Answer 1

Answer:

If I were controlling the pH of a fish tank with an Arduino, I would approach the problem differently. I would program the Arduino as follows:

1. Check the current pH.

2. If the pH is greater than some value, say 6.7, turn on the acid-controlling solenoid valve for a set duration, say 1 second (depending on flow rate, which needs to be constant, and acid concentration), or if the pH is lower than some value, say 6.3, turn on the base-controlling solenoid valve for the set duration.

3. Wait until the tank is homogeneously mixed and the pH meter has reached a steady value (you'll have to determine this time experimentally).

4. Check the new pH and calculate the change in pH.

5. Now that you know how much the pH changes for a particular solenoid actuation time, calculate how long the solenoid valve needs to be turned on to reach your target pH (6.5, for example), using a linear extrapolation.

6. Use the calculated value and actuate the solenoid valve for that duration.

7. Wait until the tank is homogeneously mixed.

8. Repeat from Step 1.

The concentration of acid or base should be adjusted so that the change observed during the set duration of solenoid valve actuation is smaller than the difference between the upper and lower limits set in Step 2 above; otherwise, you may go into oscillations between the addition of acid and base. Alternatively, you can shorten the set duration or decrease the flow rate.

Since fish constantly produce ammonia as a waste product, the buffering capacity will change with time unless you constantly exchange the water. In addition, the presence of algae, microorganisms, and plants may convert the ammonia to nitrate, which has less buffering capacity. If you choose to acidify using phosphoric acid, you will also increase the buffering capacity with every addition. In short, the system you have is complex; thus, it is difficult to calculate how much acid or base to add to effect a particular pH change.