Question

How do you find the number of grams in 1.204 moles of
`NH3`?

Answer 1

`\boxed {\boxed {\sf 20.51 \ g \ NH_3}}`

Step-by-step explanation:

If we want to convert from moles to grams, we must use the molar mass. This values tells us the mass of 1 mole of a substance. They can be found on the Periodic Table; they are equivalent to the atomic masses, but the units are grams per mole (g/mol) instead of atomic mass units (amu).

1. Molar Mass

We have the compound ammonia or NH₃. Look up the molar masses for the individual elements.

• Nitrogen (N): 14.007 g/mol
• Hydrogen (H): 1.008 g/mol

Check for subscripts. There is a subscript of 3 after hydrogen. This means there are 3 atoms of hydrogen in 1 molecule of ammonia. We should multiply hydrogen's molar mass by 3.

• H₃= 1.008 * 3=3.024 g/mol

Add nitrogen's molar mass.

• NH₃: 14.007 + 3.024=17.031 g/mol

2. Convert Moles to Grams

Now, use the molar mass as a ratio.

`\frac {17.031 \ g \ NH_3}{1 \ mol \ NH_3}`

Since we are trying to find the mass of 1.204 moles, we multiply by that value.

`1.204 \ mol \ NH_3 *\frac {17.031 \ g \ NH_3}{1 \ mol \ NH_3}`

The units of "moles of ammonia" cancel.

`1.204 *\frac {17.031 \ g \ NH_3}{1}`

The denominator of 1 can be ignored.

`1.204 * 17.031 \ g \ NH_3`

`20.505324 \ g \ NH_3`

3. Round

The original measurement of moles has 4 significant figures, so our answer must have the same. For the number we calculated, that is the hundredth place.

• 20.505324

The 5 in the thousandth place tells us to round to 0 to a 1 in the hundredth place.

`20.51 \ g \ NH_3`

1.204 moles of ammonia is equal to 20.51 grams of ammonia.