Thursday I finally started my coral dissolving project.
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| Adding 10 mM of HCl to containers of seawater |
I had six 125 mL containers that needed to be filled with seawater and each
have a different pH, to lower the pH of seawater I needed to dilute 1 M (molar)
of HCl (hydrochloric acid) to 10 mM (millimolar) of HCl.
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| 10 mM of HCl |
I did this by finding
out how many mL of HCl was needed to be added to seawater to create 125 mL of
10 mM of HCl. Using this equation, 1000 mM HCl * Vi (mL) = 10mM * 125 mL, I found that Vi
(mL) = 1.25.
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| Adding 1.25 mL of HCl to 123.75 mL of seawater |
My control pH was 8.07, the original pH of the seawater; to get
the other five pH’s, I slowly added the 10 mM of HCl to each container, ending
up with: 7.52, 7.6, 7.78, 7.91, and 8.02.
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| Six containers of different amounts of pH |
I used pliers to cut the coral into
pieces, then I used the caliper to take three measurements of each piece, I took
a dry weight of each piece, and then I soaked them for 24 hours.
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| Cutting the coral with pliers |
After they
soaked, I took a wet weight of each piece and measured them with the caliper
again.
Finally I dropped each piece into a different container.
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| Measuring each piece of coral with caliper |
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| Weighing each piece of coral |
Tuesday I
measured the pH of seawater in each container, took a wet weight of each piece of
coral and measured each piece of coral with the caliper. All of the pH’s had
gotten lower, the weight had increased, and the caliper measurements had
decreased.
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| Measuring the pH |
For
example, my control had seawater with a pH of 8.07 and had decreased to 7.36,
while the piece of coral’s wet weight had increased from 7.0569 to 7.2715, and
the caliper measurements had decreased from 1-1.74 mm, 2-1.46 mm, and 3-3.07 mm
to 1-1.65 mm, 2-1.33 mm, and 3-3.02 mm.
I will continue to see how fast the pH of each containers water will decrease and how fast each piece of coral dissolves.
Brittnie--I'm a little confused. Your control pH became more acidic after putting your coral into it?--and the coral's wet weight increased? Does this sound counter intuitive?
ReplyDeleteWhat process is taking place that causes coral to shrink yet gain weight? Is there a precipitate forming in your container?
ReplyDeleteBrittnie--regarding your ever-decreasing pH--I found a link to some info about CO^2 reactions with CaCO3 a.k.a. Limestone (coral is limestone). Maybe this would help you/readers better understand why your pH is decreasing rather than increasing as your limestone dissolves--I think any exposure of your containers to atmospheric CO^2 automatically readjusts the equilibrium in your sample containers. http://www.uh.edu/~jbutler/kunming/carbonates.html
ReplyDeleteAnother thought--you might want to google CDOM (colored dissolved organic matter--it gives natural waters that yellowish/brownish color). Wonder if bacterial decomposition of this (respiration) is producing CO2 and reducing your pH. That would also explain the pH reduction of your control since your samples have been sealed. But still--any equilibrium processes between your containers and the atmosphere also likely plays a role.
ReplyDelete