Answer:

Step-by-step explanation:
To convert from grams to moles, the molar mass is used. This tells us the grams in 1 mole of a specific substance. It can be found on the Periodic Table.
- Magnesium (Mg): 24.305 g/mol
Use the molar mass as a ratio.

Multiply by the given number of grams.

Flip the fraction so the grams of magnesium can cancel.




The original measurement of grams has 2 significant figures, so our answer must have the same.
For the number of moles we calculated, that is the tenth place. The 5 in the hundredth place tells us to round the 8 to a 9.

45 grams of magnesium is about 1.9 moles.