Question

Which solution has the higher osmolarity: 5.0% (m/v) NaCl or 5.0% (m/v) KI ?

Answer 1

5.0% (m/v) NaCl means 5 grams of NaCl present in 100 ml solution

Molecular weight of NaCl = 58.5

Molarity of NaCl = (weight/mol.wt)x (1000/volin ml) =(5/58.5)x(1000/100)= 0.855 M

Since NaCl produces two ions in solution

NaCl ---------> Na⁺ + Cl^-

osmolarity of 5.0% (m/v) NaCl = 2 x molarity = 2 x 0.855 =1.71 osmol

5.0% (m/v) KI means 5 grams of KI present in 100 ml solution

Molecular weight of KI = 166

Molarity of KI = (weight/mol.wt)x (1000/volin ml) =(5/166)x(1000/100)= 0.30 M

Since KI produces two ions in solution

KI ---------> K⁺ + I^-

osmolarity of 5.0% (m/v) KI = 2 x molarity = 2 x 0.3 = 0.6 osmol

Therefore 5.0% (m/v) NaCl solution has the higher osmolarity than 5.0% (m/v) KI