How To Calculate Molality?

Molality describes the moles of a solute concerning the mass of a solvent, while molarity is concerned with the moles of a solute concerning the volume of a solution. So to understand more in detail, we will see the difference between Molality, Molarity and Mole Fraction. Learn all the molality characteristics and see the difference between Molarity and Molality due to the whole mass of the solution’s solutes and solvents. For example, we have shown how to calculate molality molarity and mole fraction of ki.

What is Molality?

The molecular weight of a solute in a kilogramme of solvent is determined by the molecular mass of that solute. Molality can also be referred to as molal concentration. It is a metric for determining the concentration of solutes in a solution.

Characteristic of Molality

The morality of a solution is defined as its property. Since it is a property of intensity, it will not differ from one sample to the next.

Temperature and pressure do not affect the number of moles of solute or the mass of solvent. Due to this, molality is not affected by temperature or pressure, as it is not a molar quantity.

Molality is an increase in concentration not measured by volumes, such as mass or mole fractions.

Difference between Molality and Molarity

Molality is the mass of solvent, whereas molarity is the volume of the entire solution.

The Molality is represented as the small case “m,” and Molarity is shown as the upper case “M.”

The SI unit of Molality is Moles per KG (moles/kg), and the SI unit of Molarity is Moles per litre (moles/litre)

Mass percent or weight per cent (w/w %)

To calculate mass percent, multiply the mass of solute by the mass of solution by 100. It is also referred to as weight per cent and is denoted by (w/w percent). You’ve probably seen this symbol on the back of medications and tablets. It is one of the most often used units of concentration representation.

How to calculate Molality and Molarity?

In the case of Molality, you have to calculate the number of moles of solute first, then divide it by the amount of solvent in kg.

Molality = no. of moles of solute/mass of solvent in kg

In the case of Molarity, you also have to calculate no. of moles of solute but divide it by the volume of solution in litres.

Molarity = no. of moles of solute/volume of solvent in litres

How to Calculate Molality Molarity and Mole Fraction of ki

Let’s calculate Molality Molarity and mole fraction of ki for 30 per cent of (mass/mass) aqueous KI of 1.202 gm per millilitre

First, we have to calculate the mole of solute

Molar Mass of KI = 39 +127 = 166 gm per mole

30 percent of (mass/mass)  aqueous solution means 30 g of KI is present in 100g of solution

Mass of Solvent = (100-30) = 70 g

No. of moles of solute = 30/166= 0.180

Therefore,

Molality = no. of moles of solute/ mass of solvent in kg

Molality = 0.180/0.07

Molality = 2.57 m

Let’s Calculate the Molarity

Given, 

 the density of the solution= 1.202 gm per millilitre

The volume of solution = 100gm/1.202 gm per millilitre

                                    = 83.19 ml = 0.083 litre

Molarity = 0.180/ 0.083

Molarity = 2.16 M

Now its to calculate the Mole fraction of a solution

As we have calculated, the no. of moles = 0.180 mole

Moles of water = 70/18= 3.88 mole

Therefore,

Mole fraction = Moles of KI/moles of ki+moles of water

Mole fraction= 0.180/0.180+3.88

                     = 0.044

Conclusion

The mole fraction of any solution component is the ratio of the number of moles of that component present in the solution to the total number of moles of all solution components. The total solvent moles contained in a solvent kilogram are molality.

The solution’s molality is always higher than the molarity. We compute mol per unit L (i.e., the volume of solution) in molarity, whereas we calculate moles per unit Kg in molality (i.e., the mass of solvent). In any case, the mass of the solvent is smaller than the volume of the solution, resulting in a higher molality.