How many molecules in 98.40 g of water, H2O? (MM of H2O = 18.02 g/mol; 1 mol=6.02 x 1023 molecules)

1.635

⋅

10

24

molecules

Explanation:

In order to figure out how many molecules of water are present in that

48.90-g

sample, you first need to determine how many moles of water you have there.

As you know, a mole is simply a very large collection of molecules. In order to have one mole of something, you need to have exactly

6.022

⋅

10

23

molecules of that something - this is known as Avogadro's number.

In order to get to moles, you must use water's molar mass. A substance's molar mass tells you the mass of one mole of molecules of said substance.

Water has a molar mass of

18.015 g/mol

. This means that one mole of water molecules has a mass of

18.015 g

.

So, to sum this up,

6.022

⋅

10

23

molecules of water will amount to

1 mole

of water, which in turn will have a mass of

18.015 g

.