Molarity Calculator

Molarity Calculator

Molarity is the most common solution concentration in calculations dealing with volumetric stoichiometry. The units of molarity, mol/L, are represented by a scripted capital “M”. Molarity is affected by temperature because it is based on the volume of the solution, and the volume of a substance will be affected by changes in temperature.

Molarity (M) = moles solute / liters of solution = n_solute/ V_solution

Solvent: the liquid in which a solute dissolves
Solute: the substance that dissolves in a liquid to form a solution
Solution: is the mixture formed when a solute has dissolved in a solvent

How to Calulate the Molarity of a Solution by Hand - Example

1) Prepare 1000 mL of a 3M NaCl solution:

Molarity (M) is defined as moles of solute per liter of solution. The formula for molarity is:

M = \frac{\text{moles of solute}}{\text{liters of solution}}

We are asked to make a 3M solution of NaCl in 1000 mL (1 liter) of water.

Step 1: Calculate moles of NaCl needed

Molarity (M) = 3 M (mol/L)
Volume of solution (V) = 1000 mL = 1 L
Moles of NaCl = Molarity × Volume

\text{Moles of NaCl} = 3 \, \text{mol/L} \times 1 \, \text{L} = 3 \, \text{mol}

Step 2: Convert moles to grams

The molar mass of NaCl (sodium chloride) is 58.44 g/mol.

\text{Mass of NaCl} = 3 \, \text{mol} \times 58.44 \, \text{g/mol} = 175.32 \, \text{g}

Step 3: Procedure for preparing the solution

Weigh 175.32 g of NaCl.
Dissolve it in a small amount of distilled water.
Transfer the solution into a 1000 mL volumetric flask.
Add distilled water until the total volume reaches 1000 mL.

Calculation using the CHEMIX School Concentration and Dilution Calculator

1) Preparing 1000 mL of a 3M NaCl solution:

1.) Select Sodium chloride from the compound drop down menu.
2.) Insert 3 in the Molar (M) concentration field.
3.) Insert 1000 in the V_Solution -field

CHEMIX School Answer (Solution preparation procedure):

To prepare 1000mL of a 3 Molar sodium chloride solution:
******************************* By volume: *******************************
Put about 400
mL of water into a flask and add 175.327g of pure sodium chloride. Add water until 1000mL.
******************************** By mass: ********************************
Put about 400g of water into a flask and add 175.327g of pure sodium chloride. Add water until 1114.16g.

Fig. Concentration Calculator - Molarity Calculation Example - Screenshot from CHEMIX School

molarity
calculator example

Dilution Example: Prepare 500 mL of a 3M solution from a 5M NaCl stock solution:

The dilution formula is:

M_1V_1 = M_2

Where:

$M_1$ = initial molarity (stock concentration) = 5M
$V_1$ = volume of stock solution to use
$M_2$ = final molarity = 3M
$V_2$ = final volume = 500 mL = 0.5 L

Step 1: Solve for $V_1$

V_1 = \frac{M_2 \times V_2}{M_1}

V_1 = \frac{3 \, \text{M} \times 0.5 \, \text{L}}{5 \, \text{M}} = 0.3 \, \text{L} = 300 \, \text{mL}

Step 2: Procedure - Dilution

Measure 300 mL of the 5M NaCl stock solution.
Add enough distilled water to bring the total volume to 500 mL.
Mix thoroughly.

Calculation using the CHEMIX School Concentration and Dilution Calculator

1.) Select Sodium chloride from the compound drop down menu.
2.) Insert 3 in the Molar (M) concentration field.
3.) Insert 500 in the V_Solution -field
4.) Insert 5 and select Molar in the Stock concentration fields

CHEMIX School Answer (Dilution - Solution preparation procedure):

To prepare 500mL of a 3 Molar sodium chloride solution:
************ Dilution by volume ************
Put about 100mL of water into a flask and add 300mL sodium chloride stock conc. Add water until 500mL
************ Dilution by mass ************
Put about 100g of water into a flask and add 355.726g of sodium chloride stock conc. Add water until 557.081g

Fig. Dilution Calculator - Molarity Calculation Example - Screenshot from CHEMIX School

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