Randy Holmes-Farley
Reef Chemist
View BadgesStaff member
Super Moderator
Excellence Award
Expert Contributor
Article Contributor
R2R Research
My Tank Thread
- Joined
- Sep 5, 2014
- Messages
- 71,192
- Reaction score
- 68,644
Reef Chemistry Question of the Day #65
One of the fundamental questions with any salinity measuring method is how far off from normal seawater the distribution of ions can be without incorrectly messing up the measurement.
For example, many people maintain magnesium at higher than natural levels in their aquaria. Having elevated magnesium while maintaining a total salinity of 35 ppt means some other cation (e.g., sodium) must be depleted to make up the difference. That "replacement" of magnesium for some of the sodium will have an effect on all of the ways we measure salinity, but by how much? Enough to worry about?
So the question is, if we have seawater where the salinity is carefully controlled at exactly 35.00 ppt, how much will a refractometer be off in its measurement of salinity if the magnesium is actually 1500 ppm rather than the "normal" value of about 1280 ppm by replacing some of the sodium ions? Assume the refractometer is a true seawater refractometer, is accurate, and is being used at the temperature it is designed for.
A. 35.0 ppt
B. 35.1 ppt
C. 35.4 ppt
D. 36.1 ppt
E. Cannot be determined from the information given
Good luck!
.
One of the fundamental questions with any salinity measuring method is how far off from normal seawater the distribution of ions can be without incorrectly messing up the measurement.
For example, many people maintain magnesium at higher than natural levels in their aquaria. Having elevated magnesium while maintaining a total salinity of 35 ppt means some other cation (e.g., sodium) must be depleted to make up the difference. That "replacement" of magnesium for some of the sodium will have an effect on all of the ways we measure salinity, but by how much? Enough to worry about?
So the question is, if we have seawater where the salinity is carefully controlled at exactly 35.00 ppt, how much will a refractometer be off in its measurement of salinity if the magnesium is actually 1500 ppm rather than the "normal" value of about 1280 ppm by replacing some of the sodium ions? Assume the refractometer is a true seawater refractometer, is accurate, and is being used at the temperature it is designed for.
A. 35.0 ppt
B. 35.1 ppt
C. 35.4 ppt
D. 36.1 ppt
E. Cannot be determined from the information given
Good luck!
.