Relation Between Molarity And Molality - Advantages, Fundamental Definitions, FAQs

Relation between molarity and molality

Molarity and molality are terminology used to indicate the concentration of a solution, or, more simply, the amount of solute contained in a solution. Before delving into the relationship between molality and molarity, we'll go over a few basic concepts and then develop a broad relationship between the two.

Advantages

The fundamental advantage of using molality as a measurement of concentration is that molality is determined only by the masses of solute and solvent, which are unaffected by temperature and pressure changes. Volumetric solutions (e.g., molar concentration or mass concentration) on the other hand, are likely to alter as temperature and pressure change. This is a considerable advantage in many applications since the mass, or amount, of a substance is frequently more essential than its area (e.g., in a limiting reagent problem).

Another benefit of molality is that the molality of one solute in a solution is unaffected by the presence or lack of other solutes.

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Origin

Molality is derived from molarity, which is the molar concentration of a solution. The intense property molality and its adjectival unit, the now-deprecated molal, appear to have been used for the first time by G. N. Lewis and M. Randall in their 1923 publication Thermodynamics and the Free Energies of Chemical Compounds. However, the two terms are sometimes confused, the molality and molarity of a dilute aqueous solution are almost identical, because one kilogramme of water (solvent) occupies the volume of one litre at room temperature and a tiny amount of solute has minimal effect on the volume.

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Fundamental Definitions

A solution is made from a mixture, usually in liquid form, that consists of two components, namely a solute and a solvent. A solute is a little amount of a mixture's component, whereas the solvent is a big amount of the mixture's component.

A mole is a standard unit for expressing the amount of atoms or molecules of a substance present, such as water. One mole is represented by 12 grams of Carbon 12.

Molarity, also called molar concentration, is the number of moles of a solute in one litre of solution. M is used to represent it (capital m).

Molarity and molality formula is shown below.

Molarity = (number of moles of solute)/ (volume of solution (in litres)

Molality, on the other hand, is defined as the number of moles of solute contained in 1 kg (kilogramme) of solvent [The solution is made up of the solute and the solvent]. It is represented by the letter m. (small m).

Molality= (number of moles of solute)/ (weight of solvent (in kilogrammes))

Molarity and molality relation

As we can see, both molarity and molality are important characteristics for determining the concentration of a solution; therefore, a relationship between them must be established in order to calculate one parameter with the help of the other. Using the following derivation, we will attempt to establish the link between molarity and molarity:

Assume the provided solute has a mass of W x gm (W/1000 kg).

The solute's molar mass is assumed to be M' x gm.

The solvent's weight is assumed to be W' x gm (W'/1000 kg).

The volume of the solution should therefore be V ml (V/1000 l).

The solution has a molality of m.

The solution's molarity is M.

As we all know, the number of moles is symbolised by the letter X, so:

X =? (mass of the so lute taken)/ (molar mass of the solute) =W/M (1)

As a result, molarity can be stated as follows:

M = (W/M’) (V/1000) = (W 1000)/ (M’ x V) ( 2 )

And molality can be written as:

(W/M')(W'/1000) = (W 1000)/(M'W') ( 3 )

Density = mass (of solute and solvent) divided by volume = (W+W')/V (4)

Equation (2) states:

V is = (W×1000)/(M'×M), and

We can deduct from equation (3):

W' = (W ×1000)/ (M'× m)

Hence,

W + W' = W + (W× 1000)/(M× m)

We get the following result when we split density by molarity:

(Density)/Molarity= (mass of solution in kilograms) (volume of solution in litres) )/(number of moles of solute)(volume of solution in liters)

= (mass of solution in kg)/ (number of moles of solute) (volume of solution in litres)) (number of moles of solute) (5)

Density/Molarity= (mass of solution in kg)/ (number of moles of solute) = (mass of solute in kg+mass of solvent in kg)/ (number of moles of solute)(6)

Equation (6) can also be written as follows: from equation 1

Density/Molarity=(mass of solution in kg)/(number of moles of solute)=(mass of solvent in kg)/(number of moles of solute)+ (W/1000 kg)/(W/M')

Density/Molarity=(mass of solution in kg)/(number of moles of solute)=(mass of solvent in kg)/(number of moles of solute)+ M'/1000 (7)

And because we know the molality formula, equation (7) may be written as,

Density/Molarity=(mass of solution in kg)/(number of moles of solute)=1/m+ M'/1000 (8)

As a result, density/molarity (d/M) is denoted as:

(Density) / (Molarity (M) = (mass of solution in kg)/(number of moles of solute)=1/m+ M'/1000

Molarity, molality, and their link is a very important topic that is frequently questioned in both subjective and objective questions, as well as numerical style.

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