pH
The pH of seawater is very weakly buffered. That is, it is easy to shift the pH either higher [basic] or lower [acidic] very easily. The major agent of buffering in seawater is bicarbonate, but it normally only at a concentration of 2 mM. By increasing the bicarbonate concentration we can increase the buffering capacity to help the pH stay on target for our experiment.
To 500ml of seawater add 1.05 grams [a little less than 1/4 tsp.] of citric acid. Bring the pH to 5.0 and pour off 50ml into a beaker. Adjust the pH to 5.5 and pour off 50ml and so on.
TUBE# |
pH |
1 | 8.0 |
2 | 7.5 |
3 | 7.0 |
4 | 6.5 |
5 | 6.0 |
6 | 5.5 |
7 | 5.0 |
The normal pH of seawater is 8-8.3 so the pH 8 tube acts as our control. Set up five test tubes with a half inch of each of the above solutions.
- Add one drop of concentrated eggs to each.
- Swirl and let sit for one minute.
- Add one drop of diluted sperm suspension and swirl briefly.
- Wait 5 minutes.
- Score eggs for fertilization. If time permits can also score for later development [Next period see if divided. Next day see if there are swimming blastula.]