Final answer:
The chemical formula of ammonia is NH3, which includes one nitrogen atom and three hydrogen atoms. The atomic mass unit (amu) of ammonia is calculated as 17.034 amu, leading to a mass ratio of nitrogen to hydrogen of 82.23:17.77.
Step-by-step explanation:
The chemical formula for ammonia is NH3. Ammonia consists of one atom of nitrogen (N) and three atoms of hydrogen (H). To calculate the mass ratio of the combining elements in ammonia, we use their atomic masses: nitrogen has an atomic mass of 14.01 amu, and each hydrogen atom has an atomic mass of 1.008 amu.
Combining the atomic masses for the hydrogen atoms in a molecule of ammonia, we have 3 x 1.008 amu = 3.024 amu. The formula mass of ammonia can be computed by adding the mass of one nitrogen atom to the mass of three hydrogen atoms: 14.01 amu (N) + 3.024 amu (3H) = 17.034 amu for the entire NH3 molecule. To find the mass percent composition for each element, divide the mass of that element in one molecule by the formula mass of the entire molecule and then multiply the quotient by 100.
For nitrogen: (14.01 amu / 17.034 amu) x 100 = 82.23%
For hydrogen: (3.024 amu / 17.034 amu) x 100 = 17.77%
The mass ratio of nitrogen to hydrogen in ammonia by mass is therefore 82.23:17.77.