a) At physiological temperature (37 o C) the osmotic pressure of blood is 7.65 a

Question

a) At physiological temperature (37oC) the osmotic pressure of blood is 7.65 atm. If you are preparing a dextrose solution for injection, how many milligrams of dextrose (180 g/mole) do you need to add to 500 mL of sterile water to make this product isotonic with blood? (R = 0.0821 L-atm/mol-deg)?

b) When 5.2 grams of an unknown compound is added to 450 mL of water, the freezing point of the solution is – 0.28OC. What is the molecular weight of the compound? (assume i = 1; Kf = 1.86 deg-kg/mol).

c) What is the boiling point for an aqueous solution containing 100 grams of NaCl in 2 Liters of water. The eubllioscopic constant of water is 0.513 deg-kg/mole, and the molecular weight of NaCl is 58.5 g/mole.

Explanation / Answer

a)

P = MRT

M = P/(RT) = 7.65/(0.082*(37+273)) = 0.3009441 M

mol = MV = 0.3009441*05 = 0.1504 mol

mass = mol*MW = 0.1504*180 = 27.072 g = 27.072*10^3 mg

b)

m = 5.2 g of x

V = 450 mL

dT = -0.28

assume

dT = Kf*m

m = mol S / kg solvent

m solvent = 450 g = 0.45 Kg

-0.28 = -1.86*mol/0.45

mol = 0.28*0.45/1.86 = 0.0677419 mol

so

MM = mass/mol = 5.2/0.0677419 = 76.761 g/mol

c)

m = 100 g of NaCl in V = 2 L

Kb = 0.513

Tb = Kb*m*i

i = 2 ions, NA+ + Cl-

mol = mass/(MW = 100/58.5 = 1.7094 mol

mas sin kg = 2 L = 2 kg

molal = 1.7094/2 = 0.8547 molal

dTB = 0.513*0.8547*2 = 0.87692 °C

100.87692 °C

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