When a person is given an intravenous fluid, the solute concentration in the flu

Question

When a person is given an intravenous fluid, the solute concentration in the fluid must be matched to the solute concentration in the blood to avoid problems arising from a change in the blood's osmotic pressure. One such fluid, called "isotonic saline," can be made by adding salt (NaCl) to distilled water. The osmolarity of the blood is about 0.3 osmole. How many grams of NaCl must be added to a liter of water to make isotonic saline? What fraction of the solution's mass is NaCl? Repeat for dextrose, C6H12O6, which does not dissociate.

Explanation / Answer

blood O.P = 0.3

(a) for isotonic NaCl osmolysis should be equal to blood osmotic pressure

   osmotic pressure of NaCl should be equal to 0.3

P = i x M S T

i = 2 for NaCl

V = 1 litre

T = 298 K room temperature

here M = n /V = n / 1 = n

S = 0.0821 L atm /mol K

0.3 = 2 x n x 0.0821 x 298

n = 6.13 x 10^-3

moles = mass / molar mass

mass = moles x molar mass

           =6.13 x 10^-3 x 58.5

           = 0.36 g

0.36 g NaCl needed for isotonic

(b)

i = 1 for dextrose

molar mass = 180 g/mol

0.3 = 1 x n x 0.0821 x 298

    n = 0.0123

mass = 0.0123 x 180

          = 2.21 g

2.21 g dextrose is needed for isotonic with blood

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