Question

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 ?

Answer 1

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

Step-by-step 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.