# Question #f9ffd

##### 1 Answer

Here's how you can approach this problem.

#### Explanation:

A compound's empirical formula tells you the **ratio** that exists between the atoms that make up said compound.

The thing to remember here is that the number of atoms of a certain element that appears in the empirical formula **must be an integer**.

The idea here is that the mpirical formula tells you the *minimum* number of atoms of each element needed to satisfy that **ratio**.

On the other hand, a compound's molecular formula tells you **exactly** how many atoms of each type are needed to form one molecule of a substance.

In water's case, you know **for a fact** that *smaller integers* that satisfy the ratio

To prove that this is also the molecular formula, you can use water's *molar mass*. A compound's molar mass tells you what the mass of **one mole** of a substance is.

So, the molar mass of water is **all the atoms** that make up one mole of water must amount to **18.015 g**.

This can be written like this

#(2 * M_("M hydrogen") + M_"M oxygen") * color(blue)(n) = "18.015 g/mol"#

The molar masses of hydrogen and oxygen are

#(2 * 1.008 + 15.999)color(red)(cancel(color(black)("g/mol"))) * color(blue)(n) = 18.015color(red)(cancel(color(black)("g/mol")))#

#18.015 * color(blue)(n) = 18.015 implies color(blue)(n) = 1#

This means that the empirical formula and the molecular formula of water are one and the same,