Question

the density of 4M solution of kcl is 1.3g/ml.calculate molality of the solution
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Answer 1

Answer:-

3.99 m

Explanation:-

Given:-

→ Molarity of the solution = 4M

→ Density of the solution = 1.3g/mL

To find:-

→ Molality of the solution

Solution:-

• Molar mass of Potassium (K) = 39g

• Molar mass of Chlorine (Cl) = 35.5g

Hence, molar mass of KCl :-

= (39 + 35.5) g

= 74.5g

The relationship between molarity and

molality is :-

=> m = 1000M/1000d - MMₘ

Where :-

• m is molality

• M is molarity

• d is density of the solution

• Mₘ is the molar mass of solute

=> m = 1000×4/ [1000×1.3 - 4×74.5]

=> m = 4000/[1300 - 298]

=> m = 4000/1002

=> m = 3.99

Thus, molality of the solution is 3.99m .

Answer 2

$\bold{Given\::}$

$\bullet$ Molarity of solution = 4M

$\bullet$ Density of solution = 1.3g/ml

$\bullet$ Molar mass of KCl = 74.5g

$\bold{To\:find\::}$ Molality

$\bold{Formula\:used\::}$

$\bullet$ number of mole = mass ÷ molar mass

$\bullet$ Molarity = number of mole of solute ÷ volume of solution ( in L)

$\bullet$ Molality = number of mole of solute ÷ mass of solvent (in kg)

$\bullet$ Density of solution = mass of solution ÷ volume of solution

$\bold{Solution\::}$

$\bullet$ number of mole of solute = Molarity × volume

Let volume of solution = 1L

Therefore,

Number of mole of solute (KCl) = Molarity × 1 = 4 mole of KCl

$\bullet$ Using, density of solution = mass of solution ÷ volume of solution

Therefore, mass of solution = density × volume of solution

{ Density of solution = 1.3g/ml ; volume of solution = 1L = 1000ml }

Putting respective values,

Mass of solution = (1.3g/ml) × 1000ml

Mass of solution = 1300g

$\bullet$ Molality = number of mole of solute ÷ mass of solvent

for finding molality , we require

$\bullet$ number of mole of solute ( here 4)

$\bullet$ mass of solvent

mass of solution = mass of solute + mass of solvent

Therefore,

Mass of solvent = mass of solution - mass of solute

Mass of solvent = mass of solution - ( number of mole of solute × molar mass of solute)

Mass of solvent = 1300 - (4×74.5)

Mass of solvent = 1300 - 298

Mass of solvent = 1002g

Mass of solvent = 1.002 kg

Putting respective values of, number of mole of solute & mass of solvent (in kg)

Molality = 4 ÷ 1.002

Molality = 3.99m

$\bold{ANSWER\::}$ = $\bold{3.99m\::}$