Mole Concept and Molar Mass

Mole Concept and Molar Masses

When determining molar mass, the first step is to write out all the elements in the molecular formula. Depending on the number of atoms in the unit cell, square brackets are used to enclose groups of atoms. The atomic masses or atomic weights of each element are then listed next to their respective element. The subscripts are then multiplied by the atomic weight of each element to determine the molar mass. The molecular mass and mole concept here will help you determine the basic things.

Molar Mass

To define the mole concept and molar mass, it is important to understand the basic concepts first. Molar mass is defined as the mass of one mole of a substance under standard conditions. It is denoted by a lower case m and is commonly expressed in g/mol (grams per mole). In theory, the molar mass is the sum of the masses of all the individual atoms, ions, or molecules in a molecule or chemical formula. 

• However, in reality, it is more complex than that as we have to  deal with various types of interactions between these atoms, ions, and molecules which can be ionic, covalent, or metallic
• It is denoted by M and has units of g/mol, although chemists often omit these units
• Strictly speaking, molar mass also refers to the mass (in kilograms) per mole of a substance, as opposed to its weight in grams
• It is one of several other ways to express a substance’s inherent mass
• In this case, it is the ratio between the substance’s molar mass and its atomic or molecular (formula) weight

Molar Mass = mass/mole = g/mol

Mole

The current definition of one mole is based on the most stable form of carbon, carbon-12. However, it turns out that you can also understand the number of atoms in a mole in terms of a very different natural standard – the nuclear mass of helium. 

• This approach reveals that Avogadro’s number is 6.022141 × 1023
• That’s not a minor difference
• In terms of the different definitions, one mole equals not 6.022 × 1023 atoms but 6.02198 × 1023 atoms
• Just as using eggs instead of atoms changed our concept of a mole, this discovery would change our understanding of a mole if we adopted it as the official standard for how many molecules are in a mole

n = N/NA

NA = Avogadro Number

N = Number of moles

N = number of elementary entities

• For Avogadro’s number to have any significance, the masses of all atoms and molecules in nature must be created equal
• All sorts of evidence suggest that this is indeed true
• Measurements of the masses of light atoms such as oxygen and hydrogen agree with the calculated mass from their constituent parts
• It’s hard to imagine that hydrogen could have been lighter or heavier than what we find now
• But most measurements made over a century ago failed to show any variation in the weights of heavier atoms
• They all tended to weigh roughly the same no matter what their atomic number was

(moles)(molar mass) → mass

Moles (grams/mole) = grams

(mass/molar mass) → moles

(grams/grams/mole) = grams(mole/grams) = moles

Mole Concept

There is a standard way of expressing amounts of substances in chemistry for use in equations and calculations. It is the mole concept, which assigns a number to the amount of substance present. 

• This follows on from the atomic mass unit and can be used in all chemical calculations
• With the mole concept and molar masses, it is important to know how they work
• The molecular mass and mole concept is not only helpful for carrying out chemical calculations but also provides essential information about how reactants and products are related
• For example, knowing that hydrochloric acid has a mass-to-volume ratio of 35 gives us a way to compare the amounts of HCl and water that react together, whether the amounts are measured in grams or milliliters

Some Important Formulas

1. Mass of 1 mole of atoms = Atomic mass in grams
2. A number of moles of atoms = Mass of elements in grams/Relative Atomic Mass
3. Mass of 1 mole of molecules = Molecular mass in grams
4. Number of moles of molecule = Mass of the substance in grams/Relative Molecular Mass
5. Mass of substance containing 1 mole of particles = Molar Mass
6. Percentage Yield = Atomic Mass of the product obtained/Theoretical mass of product obtained

Conclusion

In this material, we got to learn about the molecular mass and mole concept and how they are used to solve problems. Apart from it, the main aim of this material was to teach the students to define the mole concept and molar mass in an easy and convenient way so that they do not face any problems in the exams. With the molecular mass in this material, the understanding of the mole concept gets easier and the equations can be balanced easily now. The mole concept and molar masses class 11 topics will help you understand everything better.