# A solution with a volume of 0.25 liters contains 20 grams of hydrogen fluoride, HF. What is the molarity of the solution?

##### 1 Answer

#### Explanation:

In order to find a solution's **molarity**, you must determine how many *moles of solute* you get **per liter** of solution.

To determine the number of moles of hydrofluoric acid present in your sample, use the compound's **molar mass**. Hydrofluoric acid has a molar mass of **one mole** of this compound has a mass of

Since your sample has a mass of

#20 color(red)(cancel(color(black)("g"))) * "1 mole HF"/(20.01color(red)(cancel(color(black)("g")))) = "0.9995 moles HF"#

Now, you know that this many moles are being dissolved in

#1 color(red)(cancel(color(black)("L solution"))) * "0.9995 moles HF"/(0.25color(red)(cancel(color(black)("L solution")))) = "3.998 moles HF"#

Rounded to one **significant figure**, the molarity of the solution will be

#color(green)(bar(ul(|color(white)(a/a)color(black)("molarity HF solution" = "4 mol L"^(-1))color(white)(a/a)|)))#