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.
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._{a}B. _{b}C._{c}... is the molar mass:
Example:
Calculate the molar mass of calcium phosphate Ca_{3}(PO_{4})_{2}:
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:
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:
By repositioning you get:
5.327 n = --------- 196.9665By calculating you get:
n = 0.0273 mol5.327 g of gold represent an amount of substance of n equal to 0.0273 mol.
b. Molar volume
The molar volume V_{m} (in l / mol) the volume V (in l) of an amount of substance n is equal to 1 mol.
V (l) V_{m}: molar volume in l / mol V_{m} = --- ---- V: volume in l n (mol) n: amount of substance in molIf one knows the molar mass M and the density rho of a substance, then the molar volume V_{m} to calculate:
There is the following relationship between the volume V and the density rho of a substance:
Substituting it into the equation of molar volume we get:
V V_{m} = --- = ----- n rho *By comparing with (1) you can see that equals, by replacing you get:
V._{m} = ---- rhoIf the density rho is determined under standard conditions (certain temperature, 0 ° C and certain pressure, 1 atmosphere), the standard density rho is obtained_{n}, and the standard molar volume V_{mn}:
V._{mn} = ----- rho_{n}Examples:
gas | formula | molar mass (g / mol) | Density rho_{n} (g / l) | Molar volume V._{mn} (l / mol) |
oxygen | ||||
nitrogen | ||||
helium | ||||
hydrogen |
As can be seen from the table, the standard molar volume is V_{mn} 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 V_{m}. Under standard conditions, V is obtained for the standard molar volume_{mn}: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
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