Question

define molarity and molality

Answer 1

Molarity describes the number of moles of the substance per liter of liquid
Molality, also called molal concentration, is a measure of the concentration of a solute in a solution in terms of amount of substance in a specified amount of mass of the solvent.

Answer 2

Heya,

Here is your answer:-

Molality


Molality is also known as molal concentration. It is a measure of solute concentration in a solution. The solution is composed of two components; solute and solvent. There are many different ways to express the concentration of the solutions like molarity, molality, normality, formality, volume percentage, weight percentage and part per million.

Molality Definition

Molality is defined as the “total moles of a solute contains in a kilogram of a solvent.” The term needs to calculate the mass of solvent and moles of solute.

Molality Formula

Molality(M)=Number of moles of soluteMass of solvent in kgs

Molality(M)=g×1000W×m

Difference Between Molarity and Molality

MolalityMolarityMass of the solventVolume of the whole solutionUnit sign expressed as (m)Unit sign expressed as (M)It has units of moles/kgIt has units of moles/liter

Molality Examples

Question: Calculate the molality of a solution where 0.5 grams of toluene (C7H8) is dissolved in 225 grams of Benzene (C6H6).

Solution

Calculate the moles of given solute.

Toluene – Molecular weight = C7H8=7×12×+1×8=92 moles/gram

Using the formula:

Moles of Toluene=Mass in gramsMolecular weight=5.0 grams92 grams/mole=0.054 mole.

So, the mole of toluene is 0.054 mole.

Now calculate the kilogram of solvent.

225 grams ofBenzene1000=0.225 kilogram

As the final step, calculate the molality using the formula.

Molality(m)=Moles of TolueneMass of Benzene in grams

Molality(m)=0.054 moles0.225 kg

Molality(m)=0.24 m

Hope this helps!
@TopperA1