Question

How many liters of water are needed to make a 4.00 M solution using 75.0
grams of lithium bromide (LiBr)?

a) 0.22
b) 2.26
c) 226
c) .002

Answer 1

Answer:

0.22L

Explanation:

Given parameters:

Concentration of solution  = 4.00M

Mass of lithium Bromide  = 75g

Unknown:

Volume of water  = ?

Solution:

Concentration in terms of the molarity is the number of moles of solute in a solution.

   Molarity  = $\frac{number of moles }{volume of solution}$

let us find the number of moles first;

Number of moles  = $\frac{mass}{molar mass}$  

  Molar mass of LiBr =  7 + 80  = 78g/mol

                                 number of moles  = $\frac{75}{78}$

                                 number of moles  = 0.96moles

Volume of water  = $\frac{number of moles }{molarity}$   = 0.96/4 = 0.22L