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Finding out a weight needed to get 1mg N/L




2006

Hey, I'm doing my 3rd year dissertation project at university and need to know the following information to get started on making up the solutions. This is for a biology project monitoring competition between aquatic plants. (I did take Chemistry A-level... but it was a long time ago!). Thank you!

I need to make a 1 mgN/L, 10 mgN/L and 100 mgN/L solutions using tap water and sodium phosphate.
The volume I need to make of each is 500 ml.

I have calculated the relative atomic mass (NH4NO3) as 98 (?). I know it may involve the equations n=m/Mr and conc=weight/volume..... but pretty clueless from there. Thank you!

Jennifer Walewski
Student - Liverpool, UK



2006

Some uncertainty with the units & identity of the chemical.
Do you wish to make solutions of 1 milligram/Liter, etc. or perhaps 1 milliNormal (0.001 N), etc.?
Since it is difficult to weigh small amounts accurately, the usual technique is to prepare a more concentrated solution, say 1.000 g/L, and make stepwise dilutions using pipets and volumetric flasks.

Does sodium phosphate perhaps mean trisodium phosphate [on eBay or Amazon] dodecahydrate, Na3PO4.12H2O (FW = (380.124)? Check the bottle label for both formula and formula weight. There are also mono- and disodium phosphates. https://en.wikipedia.org/wiki/Sodium_phosphate
The formula weight of ammonium nitrate, NH4NO3, is 80.043. Relevant?

If you need quick answers, perhaps find a chemistry student.

Ken Vlach [deceased]
- Goleta, California
contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.



! Am I the only grumpy old chemist who finds it worrying that a third year student can ask a question like this?

geoff smith
Geoff Smith
Hampshire, England


thumbs down sign There's at least one grumpy old engineer who finds it worrying too! High school chemistry in the USA these days, if thousands of letters submitted to this site by students are to be believed, apparently consists of using Dr. Pepper, taco sauce, and balsamic vinegar [in bulk on eBay or Amazon] as the reagents, as if the students were still in kindergarten :-)

Chemophobia is not immune to the law of unintended consequences. When we shield students away from any actual relationship with chemicals, we shield them away from any real knowledge of them. Young students in Asia are just so far ahead of ours that it is truly frightening for our future :-(

Anyone who feels this is overstatement is welcome to simply browse around the site at the typical questions from American students vs. the far more advanced studies of Asian students. You'll be shocked; Asian high schoolers are deeply investigating chrome plating while American students are comparing pennies cleaned with Dr. Pepper vs. Gatorade as if they were still in 2nd Grade. Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




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