A snowflake contains 1.9 1018 molecules of water. How many moles of water does it contain?

Question

A snowflake contains 1.9  10¹⁸ molecules of water. How many moles of water does it contain?

Answer 1

Use dimensional analysis to convert molecules to moles using 6.02x10²³ molecules/mole

1.9x10¹⁸ molecules H₂O x 1 mole/6.02x10²³ molecules = 3.2x10^-6 moles of H₂O

Answer 2

For this problem, you will need to know that Avogadro's number (6.022x10²³) represents the amount of molecules (or atoms, particles, etc.) in one mol of a substance. Therefore:

6.022x10²³ molecules water = 1 mole water

Now that you have all the information you need, you can convert 1.9  10¹⁸ molecules of water into mols of water:

1.9  10¹⁸ molecules H₂O 1 mol H₂O

––––––––––––––––––––– x ––––––––––– = your answer in mols of H₂O!

6.022x10²³ molecules H₂O

Does this make sense?