50.3 g
Explanation:
Start by converting the number of molecules of methanol to moles by using Avogadro's constant.
9.45
⋅
10
24
molecules CH
3
OH
⋅
Avogadro's constant
1 mole CH
3
OH
6.022
⋅
10
23
molecules CH
3
OH
=
15.69 moles CH
3
OH
Now, in order to go from moles to grams, you need to use the molar mass of the compound, i.e. the mass of exactly
1
mole of methanol.
Use the molar mass as a conversion factor to get
15.69
moles CH
3
OH
⋅
32.04 g
1
mole CH
3
OH
=
50.3 g
−−−−−
The answer is rounded to three sig figs, the number of sig figs you have for the number of molecules present in the sample.