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Home > News & Articles > Difference Between Molarity and Molality: Definitions, Examples, Formula, Relation, Key Differences, and Sample Questions
Updated on 22nd June, 2023 , 5 min read
Both molarity and molality are measurements of the concentration of a chemical solution. The major distinction between the two is one of mass versus volume. The molality explains a solute's moles in relation to the mass of a solvent, whereas the molarity describes a solute's moles in relation to the volume of a solution. The molality of a solute is the number of moles per mass of a solvent, whereas the molarity is the number of moles per volume of a solution.
A mole is the standard unit for expressing the number of atoms and molecules contained in a material. One mole is represented by 12 grams of pure carbon-12 powder.
The total number of moles of solute per liter of a solution is defined as its molarity. It is determined by parameters like volume, temperature, and pressure. M represents it. It's also known as molar concentration.
Molality (m), also known as molal concentration, is the quantity of a material dissolved in a given mass of solvent. It is defined as the moles of a solute per kilogram of a solvent. Molality is also known as molal concentration. Molality has an advantage over molarity in that it is unaffected by changes in temperature and pressure because it is determined by mass rather than volume.
Below is the relation between molarity and molality
m= 1000M/1000ρ - MMâ‚ |
Where,
ρ is the density of the solution (mg/mL).
Mâ‚ is the molecular weight of the solute.
If you dissolve table salt in water, the salt is the solute and the water is the solution. The weight of one mole of sodium chloride is 58.44 grams. A one-molar solution, abbreviated as 1M, is formed by dissolving 58.44 grams of NaCl in one liter of water.
When 2.5 grams of ethanoic acid are dissolved in 75 grams of benzene.
Solution- Ethanoic acid has a molar mass of 60 g/mol.
Ethanoic acid moles = 2.5/60 = 0.0417 mol
Benzene mass in kg = 7/1000 kilogram
Ethanoic acid molality = moles of ethanoic acid/mass of benzene
= 0.0417 × 1000 / 75
= 0.556 mol/kg
M = number of moles of the solute/volume of the solution in liters.
m = Number of moles of the solute/Mass of the solution in liters.
Molarity Calculator: Here's a useful calculator for calculating the molarity of a solution.
Molality Calculator: A molality calculator may be found here.
The following table shows the difference between molarity and molality-
|
Parameters |
Molarity |
Molality |
|
Definition |
The number of moles of a solute per liter of the solution |
The number of moles of a solute per kilogram of a solvent. |
|
Symbol |
M |
m |
|
SI Unit |
mol/L |
mol/kg |
|
Measurement |
The volume of the solution is used to calculate it. |
The mass of the solvent is used to calculate it. |
|
Accuracy |
It is incorrect and untrustworthy. |
It is precise and exact. |
|
Pressure |
It is affected by any pressure change. |
Any adjustment in pressure has no effect. |
|
Temperature |
Temperature fluctuations have an impact. |
Temperature fluctuations have no effect. |
|
Also known as |
It is also called molar concentration. |
It is also called molal concentration. |
Ans. Molality = moles solute divided by kilograms solute
0.449 mol/kg = x / 2.92 kg
x = 1.31108 mol of KBr
Moles times molar mass equals grams
(1.31108 mol) (119.0023 g/mol) = 156 g KBr
Adding them up
156 g KBr + 2920 g water = 3076 g total
Ans. 1M denotes one mole of solute in one liter of solution. We can see here that the solution is a blend of solute and solvent. 1m denotes one mole of solute in one kilogram of solution. In this case, the solution is 1 liter of solvent. This means that the amount of solvent in 1 mL of solution is greater than the amount of solvent in 1 mL of solution for the same amount of solute. As a result, the concentration of 1M solutions is higher than that of 1M solutions containing the same number of moles of solute.
Ans. The stated weight of sodium ions = 138 grams.
Sodium has a molecular mass = 23 grams.
Number of sodium ion moles = 138/23 = 6 moles
1 kilogram of the specified solvent
Hence, molality is defined as the number of moles of sodium ions divided by the weight of the solvent in kilograms.
= 6/1
= 6 m
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By - Nikita Parmar 2023-08-25 09:48:44 , 11 min readAns. Molality is a function of solution mass and so has no influence on temperature change. Because of its independence from temperature, molality is a better choice for expressing solution concentrations.
Ans. Molarity, also known as molar concentration, is the number of moles of a solute in one liter of solution. M is used to represent it.
Ans. The SI Unit of Molarity is mol/L and SI Unit of Molality is mol/kg.
Ans. A mole is the standard unit for expressing the number of atoms and molecules contained in a material. One mole is represented by 12 grams of pure carbon-12 powder.
Ans. m = 1000M/1000ρ - MM₁ is the relation between molarity and molality in which ρ is the density of the solution (mg/mL) and M₁ is the molecular weight of the solute.
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