Answer to Question #115828 in General Chemistry for Jonathan

Question

2.) 0.632 g of ammonium chloride (NH4Cl) are added to a 1 L solution of water at a temperature of 73°C in a tube separated by a semi-permeable membrane. Calculate the osmotic pressure of the solution.

Answer 1

Solution:

Osmotic pressure is expressed by the formula:

Π = iMRT

where

Π is the osmotic pressure in atm

i = van 't Hoff factor of the solute

M = molar concentration in mol/L

R = universal gas constant = 0.08206 L·atm/mol·K

T = absolute temperature in K

T = 73°C + 273.15 = 346.15 K

Moles of NH₄Cl = Mass of NH₄Cl / Molar mass of NH₄Cl

Molar mass of NH₄Cl is 53.491 g/mol

Moles of NH₄Cl = (0.632 g) / (53.491 g/mol) = 0.0118 mol

Molarity of NH₄Cl = Moles of NH₄Cl / Volume of solution

Molarity of NH₄Cl = (0.0118 mol) / (1 L) = 0.0118 mol/L

The molar concentration of NH₄Cl is 0.0118 mol/L.

Ammonium chloride dissociates completely in aqueous solution to produce ammonium cation and chloride anion:

NH₄Cl → NH₄⁺ + Cl^-

Since salt (NH₄Cl) dissociates into two ions, the value of the van’t Hoff factor here is 2.

Then,

Π = iMRT

Π = (2) × (0.0118 mol/L) × (0.08206 L·atm/mol·K) × (346.15 K) = 0.67 atm

Π = 0.67 atm

Answer: 0.67 atm is the osmotic pressure of the solution.