Science Buddies: "Ask an Expert"

I'm testing the effect of pH on brine shrimp.The problem I'm having is I can't make the solution alkaline enough to mimic the earth's oceans, which is my control at a pH of 8.2. The distilled water I'm using reads a pH of 5.8 with my pH meter, and the salt that I add makes it even more acidic. I raised the pH with baking soda like a lot of online resources recommended, but I still only got it up to 7.6.
Additionally, I am unsure about how to make soultions of different pHs for my test group. I was planning on making a solution around 7.5, and one around 6. Would I just use plain salt water and then salt water with only a little baking soda?

Hi,

If you want to get the pH to 8.2 you need to add some sodium carbonate to the bicarbonate. Sodium carbonate is available in stores as 'washing soda'. You'll have to experiment with how much to add. Start out with a small amount and keep adding till you get the pH you want. If you add too much, the pH will be too high.

For your pH 7.5 solution you could use bicarbonate alone without carbonate. For pH 6.0 maybe just a small amount of bicarbonate would do it. You need to try to have the salinity of each solution approximately equal to that of seawater, about 3.5% sodium chloride.

Let us know if you still have problems making the solutions.

Sybee