Question

Calculate the osmolarity of 1 L of solution that contains 40 mEq of sodium, 20 mEq of potassium, 60 mEq of chloride and 5 % w/v of dextrose (mol wt: 180 non-electrolyte). Is the solution isotonic, hypotonic or hypertonic to plasma (290 -300 mOsm/L)

Answer 1

One equivalence of ion means 1 mole of ion. Osmolarity is defined by the molarity of particles in a solution.

The solution contains sodium ions of 40 mOsm, potassium ion of 20 mOsm, and the chloride ion of 60 mOsm.

5% w/v dextrose is present in the solution. The 1 L solution will contain, 1000 * (5/100) = 50 g of dextrose.

Molecular weight of dextrose is 180.

So, 50/180 = 277.78 mM of dextrose or 277.78 mOsm of dextrose is present.

So, the osmolarity of the solution is (40 + 20 + 60 +277.78) = 397.78 mOsm.

This is hypertonic to plasma, as plasma osmolarity is lesser than the osmolarity of the solution.