What is the Difference Between Exact Mass and Molecular Weight

Thekey difference between exact mass and molecular weightis that exact mass is the average mass of the atoms of an element measured in theatomic mass unit, whereas molecular weight is the collection of weights of all the atoms in a molecule.

Exact mass and molecular weight are important terms at the atomic level. We can describe these terms under general chemistry, where we need calculations regarding the physical properties of atoms.

CONTENT

1.Overview and Key Difference
2.What is Exact Mass
3.What is Molecular Weight
4.Exact Mass vs Molecular Weight in Tabular Form
5.摘要 - 精确质量与分子量

What is Exact Mass?

Exact mass can be defined as the average mass of the atoms of an element measured in an atomic mass unit. It is also known as weight average molecular weight. Weight average molecular weight is the weight fraction of molecules in a polymer sample. It is another way of determining themolecular massof a polymer. It gives the average of the molecular masses of the individual macromolecules in the polymer sample. We can find this parameter using the following equation:

Mw = ∑ NiMi2 / ∑ NiMi

其中MW是平均分子量的平均分子量，Ni是分子质量Mi的分子数。我们可以使用静态光散射，小角度的中子散射，X射线散射和沉降速度来确定此参数。更重要的是，重量平均分子量总是大于平均分子量，因为样品中的较大分子的重量大于较小的分子。

What is Molecular Weight?

Molecular weight can be defined as the collection of weights of all the atoms in a molecule. The SI unit of this parameter is gmol-1. The molecular weight is the amount of atoms/molecules/compounds present in one mole of the substance. This means that it is the mass of Avogadro’s number of atoms/molecules or compounds.

It is important to measure the weight of atoms and molecules in a practical scenario. But it is difficult to weigh them as individual particles since their masses are extremely small according to the normal weighing parameters (grams or kilograms). Therefore, to fulfill this gap and measure the particles at a macroscopic level,molar massconcept is very useful.

Exact Mass vs Molecular Weight in Tabular Form

Figure 01: Separating Proteins by Molecular Weight

The definition of molecular weight is directly related to thecarbon-12同位素。一摩尔的12个原子的质量正好为12克，因此其摩尔质量正好为每摩尔12克。此外，我们可以通过将原子数量乘以原子的原子量来计算包含相同原子（例如O2或N2）的分子量。但是，通过添加每个原子的原子量来计算NaCl或CUSO4等化合物的分子量。

精确质量和分子量之间有什么区别？

Exact mass and molecular weight are important terms at an atomic level. We can describe these terms under general chemistry, where we need calculations regarding the physical properties of atoms. The key difference between exact mass and molecular weight is that exact mass is the average mass of the atoms of an element measured in atomic mass unit, whereas molecular weight is the collection of weights of all the atoms in a molecule.

摘要 - 精确质量与分子量

Exact mass can be defined as the average mass of the atoms of an element measured in an atomic mass unit. Molecular weight can be defined as the collection of weights of all the atoms in a molecule. The key difference between exact mass and molecular weight is that exact mass is the average mass of the atoms of an element measured in atomic mass unit, whereas molecular weight is the collection of weights of all the atoms in a molecule.