Question

What is the molarity of a solution of KCl if 1500. mL contains 149.2 grams of KCl? (Atomic mass of K = 39.10 g/mol and Cl = 35.45 g/mol)

Answer 1

Answer:

The molarity of a solution of KCl is 1.33 $\frac{moles}{L}$

Explanation:

The Molarity (M) or Molar Concentration is the number of moles of solute that are dissolved in a given volume. In other words, the molarity is the number of moles of solute per liter of solution.

Molarity is determined by the expression:

$Molarity(M)=\frac{number of moles}{volume}$

Molarity is expressed in units ($\frac{moles}{liter}$).

So in this case you need to know the number of moles. For that you must know the molar mass of KCl. You know:

• K= 39.10 g/mol
• Cl= 35.45 g/mol

So the molar mass of KCl is: KCl= 39.10 g/mol + 35.45 g/mol=  74.55 g/mol

Then the following rule of three applies: if 74.55 grams of KCl are in 1 mole, 149.2 grams of KCl in how many moles will they be?

$moles=\frac{149.2 g*1 moles}{74.55 g}$

moles= 2

So you know:

• number of moles= 2
• volume= 1500 mL=1.5 L (being 1 L=1000 mL)

Replacing in the definition of molarity:

$Molarity =\frac{2 moles}{1.5 L}$

Solving:

Molarity= 1.33 $\frac{moles}{L}$

The molarity of a solution of KCl is 1.33 $\frac{moles}{L}$