How many grams of H2O is 4.5 x 10 15 molecules? *
13 points
O 1.3 x 1039
O 1.3 x 10 -7
O 1.5 x 10 38
O1.5 x10 39
O Other

It is b, 1.3 × 10 ⁻⁷

Explanation:

We know that 1 mol of H₂O is ≈ 18g

We need to get out of molecules and into moles so that we can figure out how many grams of H₂O it would be.

Starting with what we're given, let's set up our equation:

4.5×10¹⁵ molecules × (1 mol / 6.02 × 10²³molecules) × (18gH₂O / 1 mol H₂O) = 1.345 × 10⁻⁷g H₂O

This is kept to 2 significant figures and ∴ 1.3 × 10⁻⁷

Further explanation:

We start out with molecules. We cancel it out using Avagadro's number which is 6.02 × 10²³ = 1 mol. Then, we want to get into grams which means that for 1 mol of H₂O, it is equivalent to 18g using the atomic mass units ( 2(1.008) + 15.999).

Hopefully, this helps you!