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Difference Between Molar Mass and Molecular Mass with FAQs

Difference Between Molar Mass and Molecular Mass with FAQs

Team Careers360Updated on 02 Jul 2025, 04:55 PM IST

Molar mass

Molar mass is also known by the name relative molar mass which can be defined as the smallest mass unit of any compound with respect to the one twelfth of the mass of a carbon atom.

What is the molar mass unit?

Unit of molar mass can be defined by two units one is standard unit and other one is S.I. unit. Standard unit of molar mass is gmol-1 and S.I. unit is given by Kgmol-1, S.I. unit of molar mass is rarely seen.

Molar mass can also be defined on the basis of mole concept where mole of any substance is defined as a substance or particle can be defined as containing exactly NH3=14+3×1=17u particles which may be atoms, molecules or ions where 6.02214076×1023 is known as Avogadro's number. Mole can be represented by its symbol called mol. It is generally described as the unit of measurement for amount of substance in SI where SI stands for International System of units. Mole can be easily defined on the basis of Avogadro’s number.

The number of atoms in 12g (0.012 kg) of isotope of carbon i.e. 12C equals the number of particles in 1 mole of the material. One of the most crucial facts to remember is that any substance mole always contains the same amount of entities, regardless of the substance.

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Molar mass formula

Calculating the atomic, molecular, and formula masses of atoms, molecules, and other compounds is fine, but since we can't weigh a single particle, these masses are only of limited utility. We must express chemical quantities at the macroscopic level to make mass measurements useful. Molar mass, or the mass in grams of one mole of a substance, serves as a link between the particle and macroscopic levels. The units of molar mass are grams per mole, as defined by its definition. The defining equation of molar mass in mathematics is

Molar mass = mass/mole = g/mol

Carbon-12 is directly or indirectly related to the definitions of atomic mass, mole, and molar mass. This leads to two key points which are described as:

  • The atomic mass of one carbon-12 atom is exactly 12 atomic mass units.
  • One mole of carbon-12 atoms has a mass of exactly 12 grams, and its molar mass is also exactly 12 grams per mole.

Commonly Asked Questions

Q: Why is molar mass important in stoichiometric calculations?
A:
Molar mass is crucial in stoichiometry because it allows us to convert between the number of moles and the mass of a substance. This conversion is essential for balancing chemical equations and determining the quantities of reactants and products in chemical reactions.
Q: How does the concept of molar mass relate to Avogadro's number?
A:
Molar mass is directly related to Avogadro's number. One mole of any substance contains Avogadro's number (6.022 x 10^23) of particles. The molar mass gives us the mass of this specific number of particles for a given substance.
Q: How do you calculate molar mass for a compound?
A:
To calculate the molar mass of a compound, sum the molar masses of all atoms in the molecule. For example, for H2O, add the molar mass of two hydrogen atoms and one oxygen atom: (2 x 1.008 g/mol) + (1 x 15.999 g/mol) = 18.015 g/mol.
Q: How does the periodic table help in determining molar mass?
A:
The periodic table provides the average atomic mass for each element, which is numerically equal to its molar mass in g/mol. By using these values and the chemical formula, you can easily calculate the molar mass of any compound.
Q: Can molar mass be measured experimentally?
A:
Yes, molar mass can be determined experimentally using various methods such as mass spectrometry, vapor density measurements, or colligative property experiments like freezing point depression or boiling point elevation.

Difference between molar mass and atomic mass

Carbon-12's atomic mass and molar mass are quantitatively equivalent. Only the units are different: atomic mass is measured in atomic mass units, whereas molar mass is measured in grams per mole. The atomic and molar masses of elements, molecular masses and molar masses of molecular substances, and formula masses and molar masses of ionic compounds all have the same relationship.

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Commonly Asked Questions

Q: Why is it important to distinguish between molar mass and atomic mass?
A:
It's important to distinguish between molar mass and atomic mass because they refer to different quantities. Atomic mass is the mass of a single atom, while molar mass is the mass of one mole of atoms or molecules. Understanding this difference is crucial for accurate calculations in chemistry.
Q: How does the concept of molar mass apply to solutions?
A:
In solutions, molar mass is used to calculate molarity (moles of solute per liter of solution) and other concentration units. It's essential for preparing solutions of specific concentrations and for stoichiometric calculations involving solutions.
Q: Can molar mass be used to identify an unknown compound?
A:
Yes, molar mass can be a useful tool in identifying unknown compounds. By determining the molar mass experimentally and comparing it to known values, or by using it in conjunction with elemental analysis, one can often identify or at least narrow down the possibilities for an unknown compound.
Q: Why is molar mass important in colligative properties?
A:
Molar mass is crucial in understanding colligative properties because these properties depend on the number of particles in solution, not their identity. Knowing the molar mass allows us to calculate the number of moles of solute, which directly affects properties like boiling point elevation and freezing point depression.
Q: How does molar mass affect osmotic pressure?
A:
Molar mass is inversely related to osmotic pressure. For a given mass concentration, solutions of substances with lower molar masses will have more particles and thus higher osmotic pressures compared to solutions of substances with higher molar masses.

Molecular mass

The molecular mass of a substance is defined as the sum of the mass of every single molecule present in it. We can easily calculate it by just adding the atomic mass units of the individual atoms in order to calculate the molecular mass of a molecule. Dalton is the most common unit of molecular mass, and it is symbolized by Da and one Dalton is equal to one unit i.e. 1Da=1u.

Molecular mass formula

The molecular mass can be easily calculated by multiplying the number of atoms in each molecule to the given molar mass of atoms. The quantity of mass associated with a molecule is known as its molecular mass. The mass of each atom multiplied by the number of atoms of the element present in the molecule can be computed. By taking the example of water we can define a molecular mass formula: water generally contains two atoms of hydrogen and one atom of oxygen. The average atomic mass of hydrogen multiplied by two plus the atomic mass of oxygen equals the mass of a water molecule. The molecular mass of elements is determined by the atoms that make up the molecule.

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Commonly Asked Questions

Q: Can a molecule have a fractional molecular mass?
A:
While individual molecules always have whole number masses (in amu), the average molecular mass can be a fraction due to the presence of isotopes. For example, the average molecular mass of chlorine (Cl2) is about 70.90 amu, not a whole number.
Q: How does the concept of molar mass apply to gases?
A:
For gases, molar mass is particularly important in calculations involving the ideal gas law and gas stoichiometry. It allows us to relate the volume of a gas to its mass and number of moles under specific conditions of temperature and pressure.
Q: What's the relationship between molar mass and density?
A:
Molar mass and density are related but distinct. Density is mass per unit volume, while molar mass is mass per mole. For a pure substance, you can calculate its density if you know its molar mass and molar volume (volume occupied by one mole of the substance).
Q: How does molar mass affect reaction rates in chemistry?
A:
Molar mass can influence reaction rates, particularly in solutions. Generally, molecules with lower molar masses tend to move faster and collide more frequently, potentially leading to faster reaction rates, all other factors being equal.
Q: How does molar mass relate to the concept of limiting reagent?
A:
Molar mass is crucial in identifying the limiting reagent in a reaction. By converting the given masses of reactants to moles using their respective molar masses, we can determine which reactant will be completely consumed first, thus limiting the reaction.

Difference between molar mass and molecular mass:

Molar mass and molecular mass can be differentiated on the basis of following factors:

1. Molar mass is generally referred to with the term mole whereas molecular mass is associated with mass of molecules present in a compound.

2. Molar mass is also known by the name molecular weight whereas molecular mass is known to us for determining the mass of a single molecule.

3. Molar mass is expressed in units like in g/mol for higher calculations while molecular mass is expressed in amu i.e. atomic mass unit.

4. Molar mass is generally defined as the mass of Avogadro number of atoms, molecules or compounds while molecular mass is defined as the sum of atomic masses of all the atoms which are present in the given molecule or compound.

5. In case of molar mass the measurement is given to compounds, atoms or molecules while in case of molecular mass we only determine molecules.

6. Molar mass is generally less accurate as compared to molecular mass while molecular mass is accurate and helps in higher calculations.

Is molar mass and molecular mass are same?/ Is molar mass and molecular mass same and the main examples of molar mass and molecular mass can be shown as follows:

Molar mass: The example of molar mass can be considered by taking the example of mass of 1 mole of oxygen which is 15.9994 grams which is exactly equal to molar mass which is given by 15.9994 g/mol.

Molecular mass: Molecular mass of water is just add up the hydrogen and oxygen atoms by summing them up i.e. in case of H2O hydrogen atoms are available and one oxygen atom is present and we know that the mass of a hydrogen atom is 1 u and mass of one oxygen atom is 16 u. Now molecular mass of water is calculated by:

1640229605447

Hence on the basis of these points we can easily differentiate between molar mass and molecular mass.

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Commonly Asked Questions

Q: What is the main difference between molar mass and molecular mass?
A:
Molar mass is the mass of one mole of a substance, while molecular mass is the mass of a single molecule. Molar mass is expressed in grams per mole (g/mol), whereas molecular mass is typically given in atomic mass units (amu) or daltons (Da).
Q: Can molar mass and molecular mass ever be numerically equal?
A:
Yes, molar mass and molecular mass can be numerically equal, but they have different units. For example, the molecular mass of H2O is about 18 amu, and its molar mass is about 18 g/mol. The numerical values are the same, but the units differ.
Q: How does the presence of isotopes affect molar mass and molecular mass?
A:
Isotopes affect both molar mass and molecular mass. For molar mass, the average atomic mass of each element (considering all naturally occurring isotopes) is used. For molecular mass, the mass of specific isotopes in a particular molecule is considered.
Q: Can a substance have a molecular mass but not a molar mass?
A:
No, all substances have both a molecular mass and a molar mass. Even for elements that exist as single atoms (like noble gases), we can still calculate both values. The molecular mass would be the mass of a single atom, while the molar mass would be the mass of one mole of those atoms.
Q: Why is molecular mass sometimes called formula mass?
A:
The term "formula mass" is used when referring to ionic compounds that don't form discrete molecules. It represents the mass of one formula unit of the compound, analogous to molecular mass for molecular compounds.

Frequently Asked Questions (FAQs)

Q: How does molar mass affect the specific heat capacity of a substance?
A:
Generally, substances with lower molar masses tend to have higher specific heat capacities. This is because lighter atoms or molecules can typically store more energy in their vibrations and rotations for a given temperature increase. However, other factors like bond strength also play a role.
Q: Why is understanding molar mass important for atmospheric scientists?
A:
Atmospheric scientists use molar mass in studying gas laws, calculating air density, and understanding the behavior of different atmospheric gases. It's crucial for modeling atmospheric processes, studying greenhouse gases, and analyzing air pollution.
Q: Can molar mass be used to predict the hardness of a solid?
A:
While molar mass alone doesn't determine hardness, it can provide some insights. In some cases, higher molar mass can correlate with increased hardness due to stronger intermolecular forces. However, factors like crystal structure and bond types play more significant roles in determining hardness.
Q: How does molar mass affect the properties of polymers?
A:
In polymer chemistry, the average molar mass of a polymer significantly affects its properties. Higher molar mass polymers generally have higher melting points, higher viscosity in solution, and better mechanical properties. Understanding molar mass distribution is crucial for predicting polymer behavior.
Q: Why is molar mass important in the study of reaction kinetics?
A:
In reaction kinetics, molar mass is used to convert between concentration units and to understand how molecular size affects reaction rates. It's also important in interpreting the order of reactions and in calculating rate constants.
Q: How does molar mass relate to the concept of mass spectrometry?
A:
In mass spectrometry, molar mass is crucial for identifying compounds. The mass-to-charge ratio (m/z) measured by the instrument is related to the molar mass of the molecule or its fragments. By analyzing these ratios, scientists can determine the molar mass and structure of unknown compounds.
Q: How does molar mass affect the rate of effusion of gases?
A:
According to Graham's law of effusion, the rate of effusion of a gas is inversely proportional to the square root of its molar mass. This means that gases with lower molar masses effuse more quickly through small openings than gases with higher molar masses.
Q: Why is understanding molar mass important for pharmacologists?
A:
Pharmacologists use molar mass to calculate drug dosages, determine drug concentrations in the body, and study drug metabolism. It's crucial for converting between mass and moles, which is necessary for understanding drug kinetics and dynamics.
Q: Why is understanding molar mass important for environmental scientists?
A:
Environmental scientists often deal with gas laws and solution concentrations when studying air and water pollution. Molar mass is crucial for converting between mass and moles, calculating gas volumes, and determining concentrations of pollutants in various environmental matrices.
Q: How does molar mass relate to the concept of molarity?
A:
Molar mass is essential for calculating molarity, which is the number of moles of solute per liter of solution. To determine the number of moles from a given mass of solute, you need to use its molar mass. This is crucial for preparing solutions of specific concentrations.
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