What is the molecular weight of rb2cr2o7

Difference between molar mass and molecular weight

Key difference - molar mass vs. molecular weight

Molecules are substances that are formed by combinations of the same or different atoms in different proportions. These molecules can be bound together to form compounds. Almost all chemical reactions are involved; the changes occur in molecules or compounds. Therefore, it is very important to understand the chemical and physical properties of molecules in order to carry out chemical reactions and predict the end products. Molecular weight and molecular weight are two such physical properties of substances. The main difference between molecular weight and molecular weight is that Molar mass indicates the mass of one mole of a certain substance whereas Molecular weight is the mass of a molecule of a given substance.

Important areas

1. What is molar mass?
- Definition, formula, units, calculation
2. What is the molecular weight?
- Definition, formula, units, calculation
3. What is the difference between molar mass and molecular weight?
- Comparison of the main differences

Key Terms: Atoms, Carbon, Isotope, Molecular Weight, Mol, Molecular Weight


What is molar mass?

Molecular mass is the mass of one mole of a given substance. It is a physical property of substances. Molecular mass is obtained by dividing the mass of a given substance by the amount of it.


The SI unit for molar mass is kg mol-1 or kg / mol. In general, however, it is given in the unit gmol-1 or g / mol.

The molar mass of an element is the atomic mass of that element. Therefore, the molar mass of a substance can be calculated by adding the atomic masses of each element present in that molecule.

Calculation of the molar mass

Let's calculate the molar mass of H2O connection.

H2O:

  • Number of hydrogen atoms present = 2
  • Atomic mass hydrogen = 1.00794 g / mol
  • Number of oxygen atoms present = 1
  • Atomic mass of oxygen = 15.999 g / mol
  • Hence the molecular weight of H2O = (2 x 1.00794 g / mol) + (1 x 15.999 g / mol)

= 18.01488 g / mol

This simple calculation indicates that the mass of one mole of H.2O compound is 18 g.

What is the molecular weight?

The term molecular weight can be defined as the mass of a molecule. It's also called that relative molecular weight. This is because molecular weight is calculated as mass relative to the carbon-12 isotope.

A hypothetical molecule called A.


The above equation indicates that the molecular weight has no units; This is because the division is between two masses that have the same units. Therefore, the molecular weight is given in terms of atomic mass units or amu. With the above equation we can find the molecular weight of an element or compound. Therefore, as in molar mass, the molecular weight of a given molecule is equal to the sum of the atomic masses of each element.

Calculation of the molecular weight

If we look at the same example, H2O,

  • The number of hydrogen atoms present is 2
  • The number of oxygen atoms present = 1
  • Mass of a hydrogen atom = 1.00794 amu
  • Mass of an oxygen atom = 15,999 amu
  • Hence the molecular weight of H.2O = (2 x 1.00794 amu) + (1 x 15.999 amu)

= 18.01488 amu

This indicates that both the molar mass and the molar mass are the same in their values, but differ in their units.


Figure 1: Phosphine The molar mass of phosphine is 33.99758 g / mol. The molecular weight is 33.99758 amu.

Difference between molar mass and molecular weight

definition

Molar mass: Molecular mass is the mass of one mole of a given substance.

Molecular weight: The term molecular weight can be defined as the mass of a molecule.

units

Molar mass: The unit of molar mass is kg mol-1 (or kg / mol).

Molecular weight: The molecular weight has no units, but is given as amu (or atomic mass units).

calculation

Molar mass: Molecular mass is calculated by dividing the mass of a substance by the amount of the substance.

Molecular weight: The molecular weight is calculated as the mass of the substance relative to 1/12th the mass of carbon-12 atom.

Conclusion

The main difference between molar mass and molecular weight is that molar mass gives the mass of one mole of a given substance, while molecular weight is the mass of a molecule of a given substance. Although the definition and units for molecular weight and molecular weight are different, the value is the same. They are physical properties of substances and very useful in chemical analysis techniques.

References:

1. Helmenstine, Anne Marie “What is molecular weight? Chemistry definition. “ThoughtCo. N.p., n. D. Netz.