Question

The molecular weight of hydrogen peroxide is 34, what is the unit of molecular weight?

Answer 1

Hint: To give the correct unit of molecular weight we should first know the correct definition of molecular weight. Think when we buy apples, it is measured in terms of kilograms. So, think when we say molar mass of hydrogen is 1 so what does it mean? Does it mean mass of one molecule of hydrogen or a specific number of molecules are taken into consideration for getting molar mass as 1. Think about Avogadro’s number and then find out the answer.

Complete step by step answer:
We should first know about the definition of molecular weight. First of all, we should ask ourselves; what do we mean by that term the weight of a molecule? Probably not since weight depends on gravity so the weight on the earth will not be the same as the weight on the moon for the same mass.
So, mass is the word we want, not weight. Now, we will know about the mass of a molecule. We should know that molecular mass (m) is the mass of a given molecule, and it is measured in Daltons (Da or u). There is one another unit that is an atomic mass unit or amu.
Now, we will clear the concept of molar mass. We should know the definition of molar mass, and it is defined as the mass of a given substance divided by the amount of a substance and is expressed in gram per mole. We use molar mass, because it is usually the more appropriate figure when we are dealing with macroscopic (weight-able) quantities of a substance.
Molecular weight or molar mass indicates mass of one mole of atoms or molecules or ions at STP, in general.
Many people when they say molecular weight actually what they are asking is molar mass. In that case, the units are gram per mole. There is one interesting thing that we should know, the amu is defined in a way that the molecular mass in amu is identical numerically to the molar mass of that molecule but with units of gram per mole.
So, let us take hydrogen peroxide molecular weight. We will use the concepts that are mentioned above:
The molecular mass of hydrogen peroxide is 34 amu or 34 Daltons.
The molar mass is 34 gram per mole.
So, now we know about the units of molecular mass and molar mass.

Note: We should know the difference between molecular mass units and molar mass units. And we should develop a habit of not saying molecular weight. We should say molecular mass and molar mass. We should note that the terms molecular mass, molecular weight, and molar mass are often used interchangeably in areas of science where distinguishing between them is unhelpful. But we should know about other areas of science in which these differences are important. We use molecular mass when we are referring to the mass of a single or specific well-defined molecule.