The term molar mass is used all the time in chemical calculations. Whether we are dealing with elements or compounds the molar mass of a species is the mass in grams of one mole (6.023 $\times$ 10
^{23}) of that species: one mole of atoms one mole of molecules or one mole of formula units.Molar mass is an extremely useful term that can be applied to any chemical species. Molar mass is the mass per mole of a substance. The units of molar mass are gmol^{-1}. For the atoms of an element the molar mass is simply the relative atomic mass g mol^{-1}. |

**"The molar mass of any substance in grams per mole is numerically equal to atomic, molecular or formula mass of that substance in atomic mass units."**

To make measurements of mass useful we must express chemical quantities at the macroscopic level. The bridge between the particulate and the macroscopic levels is molar mass, the mass in grams of one mole of a substance. The units of molar mass follow from its definition:

**grams per mole (g/mol).****Definition of molar mass**

The definition of molar mass, the mole and atomic mass are all directly or indirectly related to carbon-12.This leads to two important facts.

**The mass of one atoms of caron-12 the atomic mass of carbon-12 is exactly 12 atomic mass units.****The mass of one mole of carbon-12 atoms is exactly 12 grams its molar mass is exactly 12 grams per mole.**

Atomic mass and the molar mass of carbon-12 are numerically equal. They differ only in units. Atomic mass is measured in atomic mass units and molar mass is measured in grams per mole.

The mass of one mole of an element or compound is called its molar mass (symbol M). The molar mass of copper is 63.5 g mol

^{-1}. The molar mass of sodium hydroxide is 40 g mol^{-1}. There is a quantity that relates to the number of particles in a mass of substance. This quantity is called the amount of substance.$Amount\ of\ substance\ = \frac{Mass}{Molar\ mass}$

Molar mass equation is obtained by rearranging the above equation.

$Molar\ Mass = \frac{Mass}{Amount\ of\ substance}$

If mass is stated in g and molar mass in g mol-1, then the unit of amount is mol.

**kilogram per mole (kg/mol)**.

**Quantity symbol:**M

Mass of a substance divided by its amount of substance

$M = \frac{m}{n}$

For a mixture this term is often called

**"mean molar mass".**The molar mass is also expressed in**g mol**, but it is important to remember that in making calculations in which all other quantities are expressed in SI units the molar mass must be expressed in^{-1}**kg mol**.^{-1}**Finding molar mass**

The molar mass of a compound is the sum of the relative atomic masses of the atoms in a molecule or formula unit of the compound expressed in g mol

^{-1}.**How to calculate molar mass?**

To calculate molar mass the mass and amount of substance must be known. Below some of the molar mass examples are given.

### Solved Examples

**Question 1:**Assuming that atmospheric air is a mixture of nitrogen and oxygen in the mole ratio 79:21 estimate the molar mass of air.

**Solution:**

The mass of one mole of a substance is called molar mass.

Basis: 1 mole of air

N

_{2}present in air = 0.79 mol and O

_{2}present in air = 0.21mol

Molar mass of nitrogen = 28 $\times$ 10

^{-3}kg

Molar mass of oxygen = 32 $\times$ 10

^{-3}kg

Molar mass of air = 0.79 $\times$ 28 $\times$ 10

^{-3}+ 0.21 $\times$ 32 $\times$ 10

^{-3}

Molar mass of air = 28.84 $\times$ 10

^{-3}kg

**Question 2:**What is the molar mass of glucose C

_{6}H

_{12}O

_{6}?

**Solution:**

Sum of relative atomic mass = 6A(C) + 12A(H) + 6A(O)

Molar mass = (6 $\times$ 12) + (12 $\times$ 1) + (6 $\times$ 16) = 180

Molar mass = 180 g mol

^{-1}

Take a look at the periodic table molar mass. Notice how there is a number which represents the atomic mass of each atom. Usually it is located right under the symbol for that element, like this

$_{20.18}Ne^{10}$

The molar mass tells how many grams are in a mole of atoms of that elements. So 6.02 $\times$ 10

The following diagram illustrates how to calculate the mass of atoms by using their molar masses.

The number underneath the symbol is the atomic mass of that element. For neon the atomic mass is 20.108. This number is also known as molar mass.

The molar mass tells how many grams are in a mole of atoms of that elements. So 6.02 $\times$ 10

^{23}atoms of neon will have a mass of 20.108 grams.

The following diagram illustrates how to calculate the mass of atoms by using their molar masses.

Molar mass of a compound is the mass in grams of Avogadro number of molecules of a compound. Molar masses of some compound are listed in the following table.

S.No |
Name of the molecule |
Molar mass (g/mol) |

1 |
Molar mass of water | 18.0153 |

2 |
Molar mass of NaOH | 39.997 |

3 |
Molar mass of ethanol | 46.06844 |

4 |
Molar mass of NaCl | 58.44 |

5 |
Molar mass of CO_{2} |
44.01 |

6 |
Molar mass of air | 28.97 |

7 | Molar mass of HCl | 36.46094 |

8 | Molar mass of glucose | 180.16 |

9 | Molar mass of sucrose | 342.2965 |

10 | Molar mass of H_{2}O | 18 |

11 | Molar mass of O_{2} | 31.9988 |

12 | Molar mass of N_{2} | 28.01344 |

13 | Molar mass of carbon | 12.01078 |

14 | Molar mass of acetic acid | 60.05 |

15 | Molar mass of copper | 63.5463 |

16 | Molar mass of helium | 4.002 |

17 | Molar mass of NH_{3} | 17.031 |

18 | Molar mass of aluminum | 26.98153868 |

19 | Molar mass of butane | 58.12 |

20 | Molar mass of methanol | 32.04 |

21 | Molar mass of iron | 55.845 |

22 | Molar mass of magnesium | 24.30506 |

23 | Molar mass of KCl | 74.5513 |

24 | Molar mass of CaCO_{3} | 100.0869 |

25 | Molar mass of Na_{2}CO_{3} | 105.9886 |

26 | Molar mass of methane | 16.04 |

27 | Molar mass of H_{2}SO_{4} | 98.079 |

28 | Molar mass water | 18.0153 |

29 | Molar mass of CaCl_{2} | 110.98 |

30 | Molar mass of ammonia | 17.031 |

31 | Molar mass of silver | 107.8682 |

32 | Molar mass of acetone | 58.08 |

33 | Molar mass of argon | 39.948 |

34 | Molar mass of calcium | 40.08 |

35 | Molar mass of benzene | 78.11 |

36 | Molar mass of aspirin | 180.157 |

37 | Molar mass of sodium | 22.989 |

38 | Molar mass of hexane | 86.18 |

39 | Molar mass of H_{2} | 2.0158 |

40 | Molar mass of urea | 60.06 |

41 | Molar mass of zinc | 65.41 |

42 | Molar mass of NaHCO_{3} | 84.007 |

43 | Molar mass of sulfur | 32.065 |

44 | Molar mass of benzoic acid | 122.12 |

45 | Molar mass of CuSO_{4} | 159.62 |

46 | Molar mass of chlorine | 35.453 |

47 | Molar mass of salicylic acid | 138.121 |

48 | Molar mass of CO | 28.010 |

49 | Molar mass of potassium | 39.10 |

50 | Molar mass of KOH | 56.1056 |

51 | Molar mass of NH_{4}Cl | 53.4917 |

52 | Molar mass of iodine | 253.8 |

When the formula weight of an ionic compound is determined by the addition of its component relative atomic masses and expressed in grams, it is called the molar mass. Some of example problems are given below.

### Solved Examples

**Question 1:**Find the molar mass of a gas when the density is given as 1.25 g/L.

**Solution:**

Since it is known that 1 mol of a gas occupies 22.4L at STP we can solve this problem by multiplying the mass of 1L by 22.4 L/mol.

$\frac{1.25\ g}{L} \times \frac{22.4\ L}{1\ mol}$ = 28 g/mol

Even if the weight given is not for 1L, the same setup can be used.

**Question 2:**Find the molar mass of 1 mole of H

_{2}SO

_{4}.

**Solution:**

The molar mass id equivalent to the mass of 1 mole of that compound expressed in grams.

2 H = 1.00794 $\times$ 2 = 2.01588

1S = 32.066

4 O = 15.9994 $\times$ 4 = 63.9976

1 mole of H

_{2}SO

_{4}= 2.01588 + 32.066 + 63.9976 = 98.07 g/mol