Question

15.8g of KMNO is dissolved in 2kg of water. What is the molality
of the solutions (Atomic masses. K= 39, Mn = 55,0=16)​

Answer 1

Correct question :

15.8g of KMnO₄ is dissolved in 2kg of water. What is the molality of the solutions (Atomic masses. K= 39, Mn = 55,0=16)

Given :

• Mass of KMnO₄ = 15.8g
• Weight of water = 2kg

To find :

Molality of solution

Formula used :

• Number of mole = mass ÷ molar mass
• Molality = Number of moles of solute ÷ Weight of the solvent { in kg }

Solution :

First of all we need to find molar mass of KMnO₄

Molar mass of KMnO₄ = ( 1 × Atomic mass of K )+ (1× Atomic mass of Mn ) + (4× Atomic mass of O)

Molar mass of KMnO₄ = (1×39) + (1×55) + (4×16)

Molar mass of KMnO₄ = ( 39 + 55 + 64)

Molar mass of KMnO₄ = 158 g/mol

Number of mole of KMnO₄ = mass ÷ molar mass

Number of mole of KMnO₄ = 15.8 g ÷ 158 g/mol

Number of mole of KMnO₄ = 0.1 mol

Molality = Number of mole of KMnO₄ ÷ Mass of solvent in Kg

Molality = 0.1 ÷ 2

Molality = 0.05 m

Solution :

Molality of solution = 0.05m