Question

How many molecules of H₂O are

equivalent to 97.2 g H₂O?
(H = 1.008 g/mol, O = 16.00 g/mol)
[?]
[?]x10 molecules
Enter your answer with the correct number of
significant figures and be sure the prefix is a number
between 1 and 10!
dro's Number = 6.02 x 1023 molecules/mole

Answer 1

3.25 x 10²⁴ molecules H₂O

Step-by-step explanation:

To find the number of H₂O molecules, you need to (1) convert grams to moles (via molar mass) and then (2) convert moles to molecules (via Avogadro's Number). It is important to arrange the ratios/conversions in a way that allows for the cancellation of units. The final answer should have 3 sig figs to match the amount of sig figs in the given value.

Atomic Mass (H): 1.008 g/mol

Atomic Mass (O): 16.00 g/mol

Molar Mass (H₂O): 2(1.008 g/mol) + 16.00 g/mol

Molar Mass (H₂O): 18.016 g/mol

Avogadro's Number:

6.02 x 10²³ molecules = 1 mole

97.2 g H₂O 1 mole 6.02 x 10²³ molecules
------------------ x ------------------- x ------------------------------------ =
18.016 g 1 mole

= 3.25 x 10²⁴ molecules H₂O