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How to Calculate the Percentage by the Mass of Hydrogen in Ammonium Sulfate

Ammonium sulfate is most commonly used as a fertilizer, especially for alkaline or basic soils. It adds nitrogen, a vital plant nutrient, to the soil, and also decreases its pH by adding a small amount of acid. The chemical formula for ammonium sulfate is (NH4)2SO4. Calculating the percentage of hydrogen by mass is the same as calculating the percentage of any element in a compound. You must first properly interpret the chemical formula to determine which atoms are present and in what quantities.

Things You'll Need

Periodic table of the elements
Calculator

Instructions

- 1
  Write down all the different elements in the compound. Look for the chemical symbols in the formula. Some have one letter and some have two, but all start with a capital letter. Ammonium sulfate contains nitrogen (N), hydrogen (H), sulfur (S) and oxygen (O).
- 2
  Calculate how many of each element are present in one molecule of the compound. When an element's symbol is followed by a number, that many atoms are present. When a number follows parentheses, the number is multiplied by everything in the parentheses. In this case, the "2" following (NH4) is multiplied by both the N and the H4, meaning that there are two nitrogen atoms and eight hydrogen atoms in the molecule. The "S" is not followed by a number, so there is only one sulfur atom. The "4" following the symbol for oxygen indicates that there are four oxygen atoms.
- 3
  Look up the atomic mass of each element in the periodic table and write it alongside your tally. The atomic mass of nitrogen is 14.0067; hydrogen is 1.00794; sulfur is 32.065; oxygen is 15.9994.
- 4
  Multiply the atomic mass of each element by its number of atoms in the compound. There are two nitrogen atoms, for example, so multiply 14.0067 to get 28.0134. Write these totals alongside your previous tally.
- 5
  Add all the totals from step 4 together to get the total atomic weight of the compound. Ammonium sulfate weighs 132.14 atomic mass units.
- 6
  Divide the total weight of all the hydrogens, which you calculated in step 4, by the total weight of the whole compound, which you calculated in step 5. Multiply the resulting decimal by 100. In the case of ammonium sulfate, hydrogen makes up 6.1 percent of the molecule by weight.

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