Question

Question #7908b

Answer 1

`65.0` `"g N"_2`

Explanation:

Any time you want to convert between moles and grams of a substance, you must know that substance's molar mass, which is the mass of one mole of that substance. (One mole is equal to Avogadro's number (`6.022xx10^23`) of individual particles/molecules of that substance.)

To find the molar mass of a nitrogen molecule, we'll first realize its chemical formula, which is `"N"_2`.

Most periodic tables list the molar masses (same number as atomic mass) of all the elements under their chemical symbol. For nitrogen, the molar mass is `14.01"g"/"mol"`, that is, one mole of pure nitrogen atoms has a mass of `14.01` grams.

Since there are two nitrogen atoms per nitrogen molecule, the molar mass of `"N"_2` is double that of elemental nitrogen:

`2 xx 14.01"g"/"mol" = color(red)(28.02"g"/"mol"`

Now, we can use dimensional analysis to convert between moles and grams of `"N"_2`:

`2.32` `cancel("mol N"_2)((color(red)(28.02"g N"_2))/(1cancel("mol N"_2))) = color(blue)(65.0` `color(blue)("g N"_2`

rounded to `color(purple)(3` significant figures, the amount given in the problem.

Thus, `2.32` moles of pure nitrogen gas has a mass of `color(blue)(65.0` grams.