Question

A cell has a concentration of non-permeable solutes of 310 mOsmoles/liter. Molecular weights are : NaCl = 58, Glucose= 180, Urea=60. Cell membranes are not permeable to NaCl and glucose, but are permeable to urea.

you have 1 liter of a 11.16% glucose solution. How many grams of NaCl or ml of water must you add to it to make the solution as isotonic?

Answer 1

Isotonic solutions are the solutions having same osmotic pressure

We know that osmotic pressure = CRT

Where

C = concentration = ( mass/molar mass) x ( 1000 / volume in L)

= ( 11.16 g / 180(g/mol)) x ( 1000 / 1000 mL)

= 0.062 M

R = gas constant

T = Temperature

Since NaCl is isotonic with glucose

so the concentration of NaCl is 0.062 M

0.062 M = ( mass of NaCl / Molar mass of NaCl) x ( 1000 / Volume of solution in mL)

0.062 M = ( mass / 58(g/mol)) x ( 1000 / 1000 mL)

Mass of NaCl = 3.596 g