A concentrated solution of HBr has a molarity of 11.8 M. You add 23.50 mL to a flask and then dilute with water. The mass of the final solution is 125.0 g. What is the mass percent of HBr?

The mass percent of HBr is 17.95 % m/m.

Explanation:

Hi there!

To find the mass percent of HBr, we have to find the mass of HBr present in the solution. So, let's first find how many moles of HBr are in the solution. For that, we have to find the number of moles present in the 23.50 ml of the 11.8 M solution.

We know that in 1000 ml of the concentrated solution, there are 11.8 moles HBr. Then in 23.50 ml, there will be:

23.50 ml · (11.8 mol HBr / 1000 ml) = 0.2773 mol HBr

The molar mass (the mass of 1 mol) of HBr is 80.91 g/mol.

So, if 1 mol of HBr has a mass of 80.91 g, then 0.2773 mol HBr will have a mass of (0.2773 mol HBr · 80.91 g HBr / 1 mol HBr) 22.44 g.

This quantity is present in 125.0 g of the final solution, then, in 100 g of the solution there will be (100 g solution · 22.44 g HBr / 125 g solution) 17.95 g

Every 100 g of the solution there is 17.95 g of HBr. The mass percent of HBr is 17.95 % m/m.