# Can you help me with this? Commercially available HCl contains 38% w/w (weight by weight) of acid. If density is 1.19 g/ml, calculate molality, molarity and normality of the acid solution.

##### 1 Answer

Here's how you can approach such problems.

#### Explanation:

You know that your solution is **38% w/w** hydrochloric acid. This means that *every* **100 g** of solution will contain **38 g** of acid.

To make the calculations easier, assume that you're dealing with a **1.00-L** sample of stock solution.

Use the solution's density to determine what the mass of this sample would be

Now use the known percent concentration by mass to determine how many grams of hydrochloric acid you'd get

To determine the solution's molarity, use hydrochloric acid's molar mass - this will get you the number of moles of acid present in the sample.

Since the sample has a volume of **1.00-L**, the molarity will be

To get the solution's molality, you need to know the mass of water. Since you know the mass of the solution and that of acid, you can write

The molality will thus be - **do not** forget to convert the mass of water to kilograms!

Since hydrochloric acid, **normality** will be equal to its molarity.

*equivalence factor*, in your case equal to **1**.

**SIDE NOTE** *I left the values rounded to three sig figs.*