How To Find Molar Mass From Volume: Detailed Explanations


In this article, “how to find molar mass from volume”, definition and calculation procedure of molar volume with detailed explanations are discussed briefly.

Molar mass is very important property of any chemical substance. Molar mass is defined as the total mass of any sample divided by number of moles present in that sample. Very specifically it can be said that mass of one mole substance is called molar mass. SI and cgs unit of molar mass is kilogram/mol and gram/mol respectively.

Some frequently asked questions about molar mass and molar volume are answered in this article.

How to find molar mass from molarity and volume?

In chemistry, molar volume is the volume occupied by one mole of that substance. Molar volume is mass of any substance divided by the density of that particular sample. Molar volume = molar mass/ mass density.

Molarity is basically the unit of concentration and it is expressed as mol/litre. From known molarity of any solution, number of moles of any solution can be easily calculated.

  • No of moles = Molarity (M)× Volume
  • Unit calculation = (Mol/litre)× Litre  = Mol

From the mole number the molar mass can be determined if the total mass of any sample is known. If the density is predetermined then molar volume can be calculated by dividing the molar mass with the mass density.

how to find molar mass from volume
Calculation of molar mass and molarity.
Image Credit: Wikimedia Commons

Let’s take some examples to clear the above calculation.

Example-1: A solution of sodium hydroxide (NaOH) is prepared by dissolving by 1.6g of NaOH in 500 cc of water. Determine molarity of the solution.

  • Answer: Total mass of NaOH = 1.6g.                                                                    
  •  Volume of the solution= 500 cc = (500/1000) litre= 0.5 litre.
  • Number of moles = Total mass/ molecular mass
  • =1.6g/40 g.mol-1 [Molecular mass of NaOH= 40g.mol-1]
  • =0.04 mole

Molarity of the solution= Number of moles of the dissolving solute/ Volume of the solution in litre

Molarity= 0.04 mole/0.5 litre = 0.08 mole

To know more please follow: CH2CL2 Lewis Structure Why, How, When And Detailed Facts

Example-2: A solution is given with concentration 0.5 mol/litre. Volume of the solution 200 mili litre. Calculate the mole number of the solute dissolved in the solution. 

  • Answer: Molarity of the solution = 0.5
  • Volume of the above solution= 200 mL = (200/1000) L
  • = 0.2 L

From the given formula we know that-

Molarity of the solution= Number of moles of the dissolving solute/ Volume of the solution in litre

Thus, Number of moles of the solute = Molarity of the solution× Volume of the solution in litre

= 0.5 × 0.2 = 0.1

Let’s take some examples on calculation of molar volume.

Example-3: Calculate the molar volume of a sample of the molar mass of the oxygen gas is 1.428 g/litre.

  • Answer: Molar mass of oxygen = 32g/mol

Density of the gas= 1.428 g/L

Molar volume = Molar mass/Density

                          = 32 g.mol-1/1.428 g.lit-1 =22.4 lit

To know more please read: 5+ Double Bond Examples: Detailed Insights And Facts

Example-4: Calculate the molar volume of a 6 L gas chamber containing 0.25 mol of hydrogen at room temperature and 1atm pressure.

  • Answer: Volume of the gas chamber= 6 L

No of moles of hydrogen= 0.25

Molar volume of hydrogen = Total volume/ no of moles                                                

= 6 lit/0.25 mol = 24 lit.mol-1

How to find moles from volume?

Mole is basically a measuring unit in SI of any substance. This unit measures how much molecules or atoms or ions or any other subatomic particles are present in any species. It is measured that 1 mole of any species has 6.023*1023 number of forming particles. This number is called Avogadro’s number.

For example, 5 moles of water and 5moles of ethylene glycol have same number of water and ethylene glycol molecules respectively. With that both the chemical substances have (5×6.023×1023) number of molecules.

The following steps should be maintained to calculate mole numbers from volume-

Let’s consider some examples to make clear the calculation of mole numbers from volume.

To know more please check: 4 Hydrogen Bond Examples : Detailed Insights And Facts

Example-1: Calculate the number of moles of O2 present in 16 g of oxygen.

  • Answer:  Mass of the oxygen = 16 g

Molar mass of O2 = 32 g/mol

No of moles present in 16 g of O2 = 16 g / 32 g.mol-1

                                                             = 0.5 g.mol-1

Example-2: How many numbers of mole are present in 10 ml of acetic acid (CH3COOH). Molar mass and density of acetic acid is 60.052 g/mol and 1.05 g/cm3?

Density = 1.05 g.cm-3

Formula of density = Total mass / Volume

Thus, total mass of acetic acid = (10 ml × 1.080 g)/ 1ml

                                                     = 10.5 g

Number of moles= (10.5 g ×1mol) / 60.052 g.mol-1

                               = 0.1748 mol

To know more please go through: Is HBr Ionic or Covalent : Why? How, Characteristics and Detailed Facts

Example-3: How many moles of sodium chloride (NaCl) are present in 0.5 litre of 0.4 molar NaCl solution?

  • Answer:  Molarity of NaCl solution = 0.4

Volume of the solution= 0.5 L

Number of moles of NaCl present in the solution= 0.5 L× (0.4 mol.lit-1/ 1 L solution) = 0.2 mol NaCl

Aditi Roy

Hello, I am Aditi Ray, a chemistry SME on this platform. I have completed graduation in Chemistry from the University of Calcutta and post graduation from Techno India University with a specialization in Inorganic Chemistry. I am very happy to be a part of the Lambdageeks family and I would like to explain the subject in a simplistic way. Let's connect through LinkedIn-https://www.linkedin.com/in/aditi-ray-a7a946202

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