# Can someone help me in this? Concentrated #HNO_3# has specific gravity of 1.42. It contains 69% w/w (weight by weight) of #HNO_3#. Calculate the molarity and molality of the solution?

##### 1 Answer

#### Explanation:

A liquid's **specific gravity** is simply the ratio between its density and the density of a reference liquid, more often than not water, at the same temperature.

Usually, the specific gravity for liquids is given at **1 g/mL**.

So, in other words, using the specific gravity of a concentrated nitric acid solution is simply another way of saying that its density is **1.42 g/mL**.

Now for the actual calculations. Select a **1.0-L** sample of your stock solution, then use its density to determine what its mass is.

You also know the solution's percent concentration by mass to be **69%**. This of cours implies that *every* **100 g** of solution will contain **69 g** of nitric acid.

The mass of nitric acid your sample contains will be

Use nitric acid's molar mass to determine the number of moles you have

The solution's molarity, which is defined as the number of moles of solute, in your case nitric acid, divided by the volume of the solution - in **liters** - will thus be

To get the solution's molality, which is defined s moles of solute per **kilograms** of solvent, you need to first figure out how much water you have.

Therefore, the molality will be

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