MadSci Network: Chemistry

Re: Concentration of an Ammonium Formate solution

Date: Fri Oct 20 03:29:24 2000
Posted By: Nik Streit, Grad student, Laboratory of Atmospheric Chemistry, Paul Scherrer Institute
Area of science: Chemistry
ID: 970756913.Ch

There are a few tricky points in this calculation. First and most 
important, ammonia is a gaseous species; the "ammonia" you most likely talk 
about an aqueous solution that should be called ammonia solution for 
distinction. Commercially available solutions are in the range of 22-28% of 
ammonia in water. This is also about the solubility limit of ammonia in 
water, if you increase it, the ammonia will gas out.

In addition, you mixed up the molar weights of ammonia and formic acid in 
your calculations. The easiest way to resolve the problem will be to do the 
calculations again. The densities should be considered, as they are 
significantly different from 1, with the exception of the final solution.

Ammonia, NH3, 17 g/mol
Ammonia solution, 28%, Density = 0.9
Formic acid, HCOOH, 46 g/mol, Density = 1.2, 

Ammonia solution: 2 ml * 0.9 g/ml = 1.8 g
Ammonia: 1.8 g *0.28 = 0.50 g
0.5 g / 17 g/mol = 0.29 mol

Formic acid: 2.5 ml * 1.2 g/ml = 3.05 g;
3.05g / 46 g/mol = 0.66 mol

Considering that ammonia is the limiting reactant:

Ammonium formate: 0.29 mol * 63 g/mol = 1.85 g
1.85 g / 2000 g = 0.00093

The final solution is 0.093% in 2000 ml of water. I guess you could call it 
a 0.1% ammonium formate solution.

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