# Question 5d2fc

Jan 25, 2016

$\text{42 g}$

#### Explanation:

Think about what the density of a substance tells you.

As you know, the density of a substance is defined as the mass of one unit of volume of that substance.

color(blue)("density" = "mass"/"unit of volume"

In your case, the volume is given in milliliters, and the density in grams per milliliter, so one unit of volume will be equal to $\text{1 mL}$.

A density of $\text{0.79 g/mL}$ will thus tell you that you get $\text{0.79 g}$ for every $\text{1 mL}$ of ethanol.

So, you can say that

$\text{1 mL " -> " 0.79 g}$

$\text{2 mL " -> " 0.79 g" + "0.79 g}$

$\text{3 mL " -> " 0.79 g" + "0.79 g" + "0.79 g}$
$\vdots$

and so on. In your case ,the sample of ethanol is said to have a volume of $\text{53 mL}$. This means that its mass will be equal to

53 color(red)(cancel(color(black)("mL"))) * overbrace("0.79 g"/(1color(red)(cancel(color(black)("mL")))))^(color(purple)("given density")) = "41.87 g"#

Rounded to two sig figs, the answer will be

$m = \textcolor{g r e e n}{\text{42 g}}$