# Question #17171

##### 1 Answer

Molarity: **9.9 M**

#### Explanation:

In order to determine the molarity of a **31% w/w** hydrochloric acid (muriatic acid) solution, you need to know its density.

At

To make the calculations easier, use a **1.0-L** sample of solution.

A solution's percent concentration by mass is defined as the mass of the solute, in your case hydrochloric acid, divided by the total mass of the solution, and multiplied by 100.

So, you know that your solution is **31% w/w**, which means that you get **31 g** of solute, in your case hydrochloric acid, *for every* **100 g** of solution.

Since you know what the density of the solution is, use its volume to determine its mass

Expressed in grams, this is equal to

The mass of hydrochloric acid you get from this solution is

Since molarity is defined as moles of solute per liters of solution, use hydrochloric acid's molar mass to determine how many moles you have

Therefore, the solution's molarity will be