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Molarity Formula

Concentrations of solutions in chemistry are usually expressed as molarity, which is the number of moles of solute per liter of solution. To find the molarity of a solution requires knowing the mass of dissolved solute the volume of the solution and molar mass of the solute.

"Molarity is defined as the number of moles of solute dissolved in 1 liter of solution."

Molarity Formula is given below.

Molarity Formula
Thus molarity has the units moles per liter (mol L-1). By convention, we use square brackets [ ] to represent molarity.
The molar unit is probably the most commonly used chemical unit of measurement. Molarity is the number of moles of a solute dissolved in a liter of solution. A molar solution of sodium chloride is made by placing 1 mole of a solute into a 1-liter volumetric flask. (Taking data from the example above we will use 58 grams of sodium chloride). Water is then added to the volumetric flask up to the one liter line. The result is a one molar solution of sodium chloride.

Related Calculators
Calculate Molarity Calculating Molar Mass of a Gas
Chemistry Molar Mass Calculator Molar Concentration Calculator
 

Molarity Problems

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Solved problems based on molarity are given below.

Solved Examples

Question 1: What is the molarity of a solution that contains 10.0g of HCl (molar mass 36.5g/mol) per liter of solution?
Solution:
 
First we find the number of moles of HCl equivalent to 10.0g of HCl.

10.0g HCl $\times$ $\frac{1\ mol\ HCl}{36.5g\ HCl}$ = 0.274 mol HCl

With 0.274mol dissolved per liter of solution the molarity is 0.274M in HCl.
 

Question 2: Calculate the molarity of a solution prepared by bubbling 1.56g of gaseous HCl into enough water to make 26.8mL of solution.
Solution:
 
We are given the volume of the solution in milliliters, and we can convert this to liters.

26.8mL $\times$ $\frac{1\ L}{1000mL}$ = 2.68 $\times$ 10-2L

Thus we have

Molarity = $\frac{moles\ of\ solute}{2.68 \times 10^{-2}L}$

To calculate the molarity we need to determine the moles of solute so we change the original question to "How many moles of HCl are in 1.56"

1.56g HCl $\times$ $\frac{1\ mol\ HCl}{36.5g\ HCl}$ = 4.27 $\times$ 10-2 mol HCl

Molarity = $\frac{4.27 \times 10^{-2} mol\ HCl}{2.68 \times 10^{-2}L}$

Molarity = 1.59 M HCl

 

More topics in Molarity Formula
Molar Concentration Formula Number of Moles Formula
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