# Question #485e4

##### 1 Answer

#### Explanation:

The idea here is that you need to use the given density to determine how many grams of water you get in

Once you know how many grams of water you have, you can use water's molar mass to find how many moles that sample contains, then finally use **Avogadro's number** to get the number of molecules.

So, a density of *every mililiter* of water at

Since your sample has a volume of

#2.46color(red)(cancel(color(black)("mL"))) * "1 g"/(1color(red)(cancel(color(black)("mL")))) = "2.46 g"#

Now, a substance's *molar mass* tells you exactly what the mass of **one mole** of that substance is.

In water's case, its molar mass of *every mole* of water has a mass of

If that's the case, how many moles would you get in

#2.46color(red)(cancel(color(black)("g"))) * ("1 mole H"_2"O")/(18.015color(red)(cancel(color(black)("g")))) = "0.13655 moles H"_2"O"#

Now it's time to convert the number of moles to number of molecules.

You know that **one mole** of any substance contains exactly **Avogadro's number** I mentioned earlier.

This means that you would get

#0.13655color(red)(cancel(color(black)("moles"))) * (6.022 * 10^(23)"molecules")/(1color(red)(cancel(color(black)("mole")))) = color(green)(8.22 * 10^(22)"molecules of H"_2"O"#