# Question #db9c5

##### 1 Answer

Here's what I got.

#### Explanation:

You can't actually answer this question without knowing the **density** of the solution.

The problem tells you that salt water is **by mass**, which means that for every

So you know the mass of salt present in

In order to find the *mass* of the sample, you need to know its **density**. Let's say, for example, that a

This tells you that **every**

#100 color(red)(cancel(color(black)("mL solution"))) * overbrace((rho color(white)(.)"g")/(1color(red)(cancel(color(black)("mL solution")))))^(color(blue)("the density of the solution")) = (100 * rho)color(white)(.)"g"#

So if you get

#(color(blue)(cancel(color(black)(100))) * rho) color(red)(cancel(color(black)("g solution"))) * overbrace("3.5 g salt"/(color(blue)(cancel(color(black)(100)))color(red)(cancel(color(black)("g solution")))))^(color(blue)(" = 3.5% m/m salt")) = (3.5 * rho)color(white)(.)"g salt"#

Now, a sodium chloride solution at room temperature that is

#rho = "1.02 g mL"^(-1) -># seehere, at the bottom of the page.

This means that you will have

#"mass of salt" = (3.5 * 1.02)color(white)(.)"g" = "3.6 g salt"#

I'll leave the answer rounded to two **sig figs**, but keep in mind that you have one significant figure for the volume of the solution.