Question

(2 points if turned in on time): An aqueous solution of hydrobromic acid, HBr,r has a density of 1.50 g/mL and is 48.0% by weight HBr. Calculate the molarity of this solution. Show all work.

Answer 1

Let volume of solution be 1 L

volume , V = 1 L

= 1*10^3 mL

density, d = 1.5 g/mL

use:

mass = density * volume

= 1.5 g/mL *1*10^3 mL

= 1.5*10^3 g

This is mass of solution

mass of HBr = 48.0 % of mass of solution

= 48.0*1500.0/100

= 720.0 g

Molar mass of HBr,

MM = 1*MM(H) + 1*MM(Br)

= 1*1.008 + 1*79.9

= 80.908 g/mol

mass(HBr)= 720.0 g

use:

number of mol of HBr,

n = mass of HBr/molar mass of HBr

=(7.2*10^2 g)/(80.91 g/mol)

= 8.899 mol

volume , V = 1 L

use:

Molarity,

M = number of mol / volume in L

= 8.899/1

= 8.899 M

Answer: 8.90 M