How to Calculate the Amount of Nitrogen in Ammonia
Ammonia is a molecular compound with the formula NH3. At room temperature it's a gas but dissolves readily in water, where it acts as a base and increases the pH. Household ammonia is a solution of ammonia in water. Since the ammonia molecules can accept hydrogens from water molecules, some of the ammonia in the solution will be present in the form of the conjugate acid, the ammonium ion (NH4+). Ammonia is important in the manufacture of fertilizers since it contains nitrogen.
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Instructions
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Determine the concentration of ammonia in the solution (i.e. the number of moles per liter). If you are conducting this experiment as part of a chemistry lab or for a product evaluation, perform a titration to find the concentration. Instructions for titration are beyond the scope of this article; the website listed under the Resources section at the bottom of this page provides more details. Alternatively, if you are working this as a problem on homework in a chemistry class, the concentration will typically be specified in the instructions for the problem.
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Multiply the concentration of ammonia in the solution by the total number of liters of solution. This equation will give you the total number of moles of ammonia.
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Multiply the number of moles of ammonia by the number of grams per mole for nitrogen as specified on the periodic table. This equation will give you the total number of grams of nitrogen in the solution.
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Tips & Warnings
Ammonia is a weak base with a Kb of 1.8 x 10 to the -5. This number gives the ratio of ammonia to ammonium and hydroxide ions in solution via the formula 1.8 x 10 to the -5 = [OH-] [NH4+] / [NH3], where brackets indicate concentrations. The pH of a solution is equal to 14 minus the pOH, and since pH = -log [H+], 10 to the pH = [H+], so you can use the pH to find the [OH-] value in this equation. If you're trying to find the pH of an ammonia solution and only know the starting concentration of ammonia, you can work backward by using A as the starting concentration and x as the amount of ammonia that accepts a hydrogen ion to become NH4. The equation is then rewritten as follows: 1.8 x 10 to the -5 = (x) (x) / (A - x) and solve using the quadratic formula to find x. The pH will then be 14 - (-log x).
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