# How many molecules are in 48.90 grams of water?

##### 1 Answer

#### Answer:

#### Explanation:

In order to figure out how many *molecules* of water are present in that *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 **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 **one mole** of water molecules has a mass of

So, to sum this up,

So, use water's molar mass to find the number of moles present in that sample

#48.90 color(red)(cancel(color(black)("g"))) * ("1 mole H"_2"O")/(18.015color(red)(cancel(color(black)("g")))) = "2.7144 moles H"_2"O"#

Now use Avogadro's number to find the number of molecules of water

#2.7144 color(red)(cancel(color(black)("moles H"_2"O"))) * (6.022 * 10^(23)"molec.")/(1color(red)(cancel(color(black)("mole H"_2"O")))) = color(green)(1.635 * 10^(24)"molec.")#

The answer is rounded to four sig figs, the number of sig figs you have for the mass of water.