How To Find Mass From Moles And Molar Mass: Detailed Explanations


In this article we are going to analyze how to find mass from moles and molar mass.

Finding mass from moles and molar mass is very simple. It can be done by using the relation given below:

Where,

how to find mass from moles and molar mass
how to find mass from moles and molar mass

n = is the number of moles (mol)

m = is the mass in grams (g)

M = is the molar mass (g/mol)

We can understand it better by solving some examples:

How to find mass from moles and molar mass examples:

1.Calculate mass of O2 having moles equal to 10.2 mol.

Solution:

Molar mass = O2 = 16×2 = 32g/mol

n = 10.2 mol

m = n × M = 10.2 mol × 32g/mol = 326.4g

2.XYZ beach has got many minerals in its sand. SiO2 was one of them that was estimated and it had 12.5 moles, so what is the mass of SiO2 ?

Image credit: Wikimedia commons

Solution:

Molar mass = SiO2 = 28 + 16×2 = 60g

n = 12.5 moles

m = n × M = 12.5moles × 60g/mol = 750g

3.Calculate mass of 7.86 moles of Calcium Chloride?

Solution:

We know that the formula of Calcium Chloride is CaCl2.

Molar mass = CaCl2 = 40 + 35.45×2 = 110.90 g/mol

n = 7.86 moles

m = n × M = 7.86 moles × 110.90 g/mol = 871.674g

4.A student in laboratory prepared 6.8 moles of KNO3 and used it for titration so in order to proceed with the calculations what will be its mass ?

Solution:

Molar mass = KNO3 = 39 + 14 + 3×16 = 110 g/mol

n = 6.8 moles

m = n×M = 6.8 mol × 110 g/mol = 748g

5.Calculate mass of FeCl3 having moles equal to 5.7 moles.

Solution:

Molar mass = FeCl3 = 55.845 +35.453×3 = 162.204 g/mol

n = 5.7 moles

m = n × M = 5.7 × 162.204 = 924.562 g

6.Calculate mass of 2.7 moles of Barium Sulphate.

Solution:

Molar mass = BaSO4 = 137.33 + 32.06 + 64 = 233.39 g/mole

n = 2.7 moles

m = n × M = 2.7 × 233.39 = 630.153g

7.Calculate the mass of 3.98 moles of strontium chloride.

Solution:

Molar mass = SrCl2 = 87.62 + 35.453 + 35.453 = 158.52 g/mol.

n = 3.98 moles

m = n × M = 3.98 × 158.52 = 630.90g

8.Calculate the mass of 4.32 moles of Ammonium Phosphate.

Solution:

Molar mass = (NH4)3PO4 = 14.01 × 3 + 12 + 30.97 + 16 = 149.12 g/mol.

n = 4.32 moles

m = n × M = 4.32 × 149.12 = 644.198g

9.Calculate the mass of 3.7 moles Magnesium Nitrate .

Solution:

Molar mass = Mg(NO3)2 = 24 + 2×14 + 6×16 = 148 g/mol

n = 3.7 moles

m = n× M = 3.7 × 148 = 547.6g

10.Calculate the mass of 4.24 moles of Aluminium hydroxide.

Solution:

Molar mass = Al(OH)3 = 27 + 16×3 + 3 = 78 g/mol

n = 4.24 moles

m = n×M = 4.24 × 78 = 330.72g

11.Calculate the mass of 1.49 moles of lead(ll) iodide

Solution:

Molar mass = PbI2 = 207.2 + 253.80 = 461 g/mol

n = 1.49 moles

m = n×M = 1.49 × 461 = 686.89g

12.Calculate the mass of 5.34 moles of Magnesium Carbonate.

Solution:

Molar mass = MgCO3 = 24 +12 + 16×3 =84 g/mol

n = 5.34 moles

m = n×M = 5.34 + 84 = 448.56g

13.Calculate the mass of 6.136 moles of Arsenic acid.

Solution:

Molar mass = H3AsO4 = 3 + 74.9 + 3×16 =141.9 g/mol

n = 6.136 moles

m = n×M = 6.136 × 141.9 = 870.69g

14.Calculate the mass of 4.59 moles of Lithium Carbonate.

Molar mass = Li2CO3 = 13.88 + 12 + 3×16 = 73.89 g/mol

n = 4.59 moles

m = n×M = 4.59 × 73.89 = 339.15g

15.Calculate the mass of 4.999 moles of household bleach.

Solution:

Molar mass = NaOCl = 23 + 16 + 35.4 = 74.4 g/mol

n = 4.999 moles

m = n×M = 4.99 × 74.4 = 371.92g

16.Calculate the mass of 2.156 moles of Potassium dichromate.

Solution:

Molar mass = K2Cr2O7 = 78 + 104 + 112 = 294 g/mol

n = 2.156 moles

m = n×M = 2.156 × 294 = 633.96g

Image credit: Wikipedia

Read more about: How To Find Molar Mass From Molarity: Detailed Explanation

How to Calculate molar mass without mass ?

Usually the most common method of finding Molar mass is by using the formula M = m/n which has been discussed in the earlier section in detail.

By using the colligative properties method we can calculate molar mass without getting mass into picture.  Let us analyze how in the section followed:

Benzene is used to dissolve the substance ( the unknown one whose molar mass has to be estimated) and it is made to 1.55 % ( mass % that of unknown mixture to Benzene). The benzene’s boiling point is made to rise by around 2.3%.

Considering the colligative properties:

Actual Benzene’s boiling point = 80 degrees Celsius.

ΔT = is the change in the boiling point ( 1.84 degrees) 80 × 0.023

I = is the van’t Hoff (factor), for Benzene it is considered to be one as it is not an electrolyte.

m = is the molality

K = the constant for Benzene ( boiling point) is around 2.53.

Now,

   = 1.84/ 1× 2.53

m = 0.728 moles ( the unknown) / kg benzene

We had taken the mixture as 1.55%

So, 1.55% mass meaning 1.55g of unknown is present in per 100g of the solution.

Hence the unknown molar mass will be the ratio:

Molar mass = the one calculated from benzene method/ 0.728 moles

Sania Jakati

This is Sania Jakati from Goa. I am an aspiring chemist pursuing my post graduation in organic chemistry. I believe education is the key element that moulds you into a great human being both mentally and physically. I'm glad to be a member of scintillating branch of chemistry and will try my best to contribute whatever I can from my side and Lambdageeks is the best platform where I can share as well as gain knowledge at the same time. LinkedIn-https://www.linkedin.com/in/sania-jakati-0954101bb

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