# An empty 250 mL beaker has a mass of 60 g. When 100 mL of oil is added to the beaker, the total mass is 140 g. What is the density of the oil?

##### 1 Answer

#### Explanation:

To find the density of the oil, all you have to do is figure out how many grams you get in

In that regard, the **density** of a substance is simply the mass of *one unit of volume* of said substance. Since you're working with *milliliters* here, the mass of one unit of volume will be the mass of

Now, you know that the empty beaker has a mass of

#m_"oil" = "140 g" - "60 g" = "80 g"#

Notice that you don't need to know the volume of the empty beaker to find the density of the oil; since you already know the **mass** of the oil, all you need to know is its **volume**.

The problem states that you're adding

#1 color(red)(cancel(color(black)("mL"))) * "80 g"/(100color(red)(cancel(color(black)("mL")))) = "0.80 g"#

This means that the density of the oil,

#color(darkgreen)(ul(color(black)(rho = "0.8 g mL"^(-1)))) -># every milliliterof oil has a mass of#"0.8 g"#

The answer is rounded to one **significant figure**.