In this article, we learn about the how to calculate molar mass from pressure of gas molecules and how it can be calculated from pressure, volume, density, and detailed facts.

**A molecule containing one mole of its own substance is called the molar mass of that particular substance. In simplification, it is the weight of one mole of a substance. By the help of Avogardo’s number we can calculate molar mass**.

It is denoted by the formula,

**M=m/n**, Where **m** is the molar mass of a substance in gram, **m** is the mass of a substance in a gram ,**n** is the number of moles of a substance.

**How to calculate molar mass from pressure** ?

**Using the ideal gas equation, we can easily calculate the molar mass from pressure.**

It is evident from ideal gas equation

**PV=nRT**

P= pressure of a gas, V=volume of a gas, R=universal gas constant, T= temperature, n =number of moles of a gaseous molecule.

**Again, we know**

**n =m/M = mass / Molar mass**

**so, putting the value of n in the above equation we get**

**PV=(m/M)RT**

**So, M = m(RT/PV)**

**M α 1/P** **[where α is the proportional constant]**

**So, we can say that from the above equation Molar mass is inversely proportional to the pressure of gaseous molecules. That means the higher the molar mass of gas the lower will be its pressure and vice versa**, how to calculate molar mass from pressure is important factor.

**Calculate Molar mass from temperature**

**From the ideal gas equation, molar mass can be calculated from temperature.**

**PV=nRT**

P= pressure of a gas, V=volume of a gas, R=universal gas constant, T= temperature, n =number of moles of a gaseous molecule.

**Again, we know**

**n =m/M = mass / Molar mass**

**so, putting the value of n in the above equation we get,**

**PV=(m/M)RT**

**So, M = m(RT/PV)**

**M α T****[where α is the proportional constant]**

**So, in the above relation, the relation between molar mass and temperature is directly proportional to each other. So, the higher the temperature higher will be the molar mass.** how to calculate molar mass from pressure is important factor, here but we build relationship between molar mass and temperature here.

**Calculate molar mass from Volume**

**Molar mass from Volume can be calculated by using the ideal gas equation**

**PV=nRT**

P= pressure of a gas, V=volume of a gas, R=universal gas constant, T= temperature, n =number of moles of a gaseous molecule.

**Again, we know**

**n =m/M = mass / Molar mass**

**so, putting the value of n in the above equation we get,**

**PV=(m/M)RT**

**So, M = m(RT/PV)**

**M α 1/V** **[where α is the proportional constant]**

**So, we can say that from the above equation Molar mass is inversely proportional to the volume of gaseous molecules. That means the higher the molar mass of gas the lower will be its volume and vice versa.** how to calculate molar mass from pressure is important factor, here but we build relationship between molar mass and volume here.

**Calculate molar mass from density**

**The density is equal to the mass of a substance over its volume.**

**Using the ideal gas equation, we can easily calculate the molar mass from density.**

**PV=nRT**

**Again, we know**

**n =m/M = mass / Molar mass**

**so, putting the value of n in the above equation we get,**

**PV=(m/M)RT**

**M = (m/V)(RT/P)**

**M=ρ(RT/P)**

**So, M α ρ** **[where α is the proportional constant]**

**So, density is directly proportional to the Molar mass of a gaseous molecule.** how to calculate molar mass from pressure is important factor. here but we build relationship between molar mass and density here.

**Calculate molar mass from osmotic pressure**

**Using colligative property formula to calculate the molar mass from osmotic pressure.**

From the colligative property,

**Π=iCRT**

Where Π is the osmotic pressure of a given substance, I = Vant Hoff factor (it is a constant), C= concentration of solute in a particular solution, R= Universal gas constant, and t = temperature.

For gaseous molecules, the concentration of solute in a particular solution will convert to molar mass and we omit the I factor as it is a constant term**.**

Now the equation becomes** Π=MRT.**

**So Π α M**

**[where α is the proportional constant]**

**So osmotic pressure is also directly proportional to the Molar mass of the gaseous molecule.** how to calculate molar mass from pressure is important factor. here but we build relationship between molar mass and osmotic pressure here.

**Calculate molar mass from Vapour pressure**

**From the colligative property, we know that relative lowering of vapor pressure is most suitable than vapor pressure.**

So here we not only how calculate the molar mass from pressure but also calculate molar mass of a solute from relative lowering vapor pressure.

From Raoult’s Law

**(P ^{0}-P)/P^{0} = X_{2}……(i)**

**Where P ^{0}** is the vapor pressure of pure solvent and P is the vapor pressure of the solution. X

_{2}is the mole fraction of solute.

Again, X_{2 }= n_{2/(}n_{1+}n_{2)}

For ideal solution n_{1}>>>n_{2}

So, the equation reduces to,

X_{2}=n_{2}/n_{1} ………(ii)

n_{2}=W_{2}/M_{2} and n_{1}=W_{1}/M_{1}

then the equation (ii) becomes,

X_{2}=(W_{2}/M_{2})|(M_{1}/W_{1})….(iii)

Comparing equations (i) and (iii) we get,

(W_{2}/M_{2})(M_{1}/W_{1})=(P^{0}-P)/P^{0}

**M _{2}= (W_{2}/W_{1})M_{1 }(P^{0}/p^{0}-p)**

**So, the Molar mass is directly proportional to the lowering vapor pressure of a volatile molecule.** how to calculate molar mass from pressure is important factor. here but we build relationship between molar mass and vapour pressure here.

**Frequently Asked question**

**How to calculate molar mass with ideal gas law?**

**By using the ideal gas law PV=nRT we can easily calculate the molar mass.**

By using this law, we can calculate how to calculate molar mass from pressure , the relation between molar mass and pressure, molar mass and temperature, and molar mass and volume.

**What is the basic difference between mole and molar mass?**

**Mole is defined as a number of substances per Avogadro’s number** and molar mass is one mole of that substance.

Mole is defined as n=N/N_{A}, Where N_{A} is Avogadro’s number, and the value is 6.023*10^{23}.

**How many atoms are equal to one mole?**

**One mole is equal to 6.023*10 ^{23} atoms** as it contains Avogadro’s number of atoms.

**What is the unit of molar mass?**

**Molar mass = mass of the substance (in grams)/ number of moles**

So, the unit of molar mass is **gram**/mol.

Hi……I am Biswarup Chandra Dey, I have completed my Master’s in Chemistry from the Central University of Punjab. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.