Question

Calculate the number of moles for 50.7 g of hydrogen gas

Answer 1

Answer: 50.7 moles

Step-by-step explanation:

given mass/ molecular mass

= 50.7/1

=50.7

Answer 2

`\boxed {\boxed {\sf 25.1 \ mol \ H_2}}`

Step-by-step explanation:

We are asked to calculate the number of moles in 50.7 grams of hydrogen gas. To do this, we will use the molar mass or the mass of 1 mole of a substance. These values are found on the Periodic Table because they are equivalent to the atomic masses, but the units are grams per mole instead of atomic mass units.

Look up the molar mass of hydrogen (H).

• H: 1.008 g/mol

Note that we are given grams of hydrogen gas. This is a diatomic molecule with 2 hydrogen atoms. The formula is H₂. Multiply the molar mass by 2 to find hydrogen gas's molar mass.

• H₂ = 1.008 *2 = 2.016 g/mol

Now we can convert using dimensional analysis. Set up a ratio using the molar mass.

`\frac {2.016 \ g \ H_2}{1 \ mol \ H_2}`

We are converting 50.7 grams to moles, so we multiply the ratio by this value.

`50.7 \ g \ H_2 *\frac {2.016 \ g \ H_2}{1 \ mol \ H_2}`

Flip the ratio so the units of grams of hydrogen gas cancel.

`50.7 \ g \ H_2 *\frac{1 \ mol \ H_2} {2.016 \ g \ H_2}`

`50.7 \ *\frac{1 \ mol \ H_2} {2.016 }`

`\frac {50.7} {2.016 } \ mol \ H_2`

`25.14880952 \ mol \ H_2`

The original value of grams (50.7) has 3 significant figures, so our answer must have the same. For the number we calculated, that is the tenths place. The 4 in the hundredth place to the right tells us to leave the 1 in the tenths place.

`25.1 \ mol \ H_2`

50.7 grams of hydrogen gas is equal to approximately 25.1 moles of hydrogen gas.