# What is the molar mass of oxygen

### 6.3 Molar mass and molar volume

a. Molar mass
The molar mass M (in g / mol) is the mass m (in g) of an amount of substance n equal to 1 mol.

m (g) M: molar mass in g / mol M = --- ---- m: mass in g n (mol) n: amount of substance in mol

The molar mass of an element is given in the periodic table of the elements (mass number in g / mol).
Examples:
Molar mass of copper: 63.546 g / mol.
Molar mass of gold: 196.9665 g / mol.
Molar mass of sulfur: 32.066 g / mol.
The molar mass of a compound is calculated in the same way as the molecular mass in u, but the molar masses of the elements are used:
For a chemical formula A.aB. bC.c... is the molar mass:

M (AaB.bC.c...) = a * M (A) + b * M (B) + c * M (C) + ...

Example:
Calculate the molar mass of calcium phosphate Ca3(PO4)2:

M (approx3(PO4)2) = 3 * M (Ca) + 2 * M (P) + 2 * 4 * M (O) M (Approx3(PO4)2) = 3 * 40.078 + 2 * 30.9738 + 8 * 15.9994 M (approx3(PO4)2) = 310.1768 g / mol

If you know the mass m of a substance portion, you can calculate the amount of substance n in mol.
Example:
What amount of substance in moles represents 5.327 g of gold?
The following relationship is given: m M = --- (1) n

Mass of the portion of the fabric: m = 5.327 g.
Molar mass of gold: M = 196.9665 g / mol Substituting in (1) one obtains:

5.327 196.9665 = ------- n

By repositioning you get:

5.327 n = --------- 196.9665

By calculating you get: n = 0.0273 mol

5.327 g of gold represent an amount of substance of n equal to 0.0273 mol.

b. Molar volume

The molar volume Vm (in l / mol) the volume V (in l) of an amount of substance n is equal to 1 mol.

V (l) Vm: molar volume in l / mol Vm = --- ---- V: volume in l n (mol) n: amount of substance in mol

If one knows the molar mass M and the density rho of a substance, then the molar volume Vm to calculate:
There is the following relationship between the volume V and the density rho of a substance:

m V = --- rho

Substituting it into the equation of molar volume we get:

V Vm = --- = ----- n rho *

By comparing with (1) you can see that equals, by replacing you get:

V.m = ---- rho

If the density rho is determined under standard conditions (certain temperature, 0 ° C and certain pressure, 1 atmosphere), the standard density rho is obtainedn, and the standard molar volume Vmn: V.mn = ----- rhon

Examples:

 gas formula molar mass (g / mol) Density rhon (g / l) Molar volume V.mn (l / mol) oxygen nitrogen helium hydrogen As can be seen from the table, the standard molar volume is Vmn the same for very different gases. This statement can be further generalized:
At the same temperature and pressure, all gases have the same molar volume Vm. Under standard conditions, V is obtained for the standard molar volumemn: V.mn = 22.4 l / mol

If you know the molar mass or the molar volume of a substance, you can calculate the optimal mass ratios of the starting materials of a chemical reaction. It is also possible to calculate the mass of products you get:
6.4 Calculations on molar sizes Back to quantitative relationships Back to the table of contents