Hi all, I having particular trouble with a problem that revolves around isotonicity and freezing point depression. Any help would be appreciated.
6) Zinc & Adrenaline Eye Drops
Zinc Sulphate 0.25g
Adrenaline 0.02g
Boric acid as required
Glycerol 1 mL
Purified water to 100mL
Use the following information to make 25.0mL of these eye drops for a patient and calculate the required amount of boric acid required to make the solution isotonic.
You already have an adrenaline 1:1000 solution that is isotonic (assume this is used to make up the eye drops).
FD1% Zinc Sulphate = 0.086 °C
FD1% Boric acid = 0.288 °C
FD1% Glycerol = 0.203 °C
Express your answer in milligrams to 3 significant figures.
Worked Answer:
Zinc Sulphate 0.25 %(w/v)
Adrenaline 0.02g
Boric acid as required
Glycerol 1 %(v/v)
Purified water to 100mL
So, we need it to be isotonic so Freezing point must be -0.52oC
0.52- (0.086/4) - 0.203 = 0.2955
than divide by FD1% Boric acid
0.2955/0.288 = 1.026%(w/v) of Boric Acid
The questions asks for Boric acid in 20mL
Adrenaline is already isotonic, find it's volume in 20mL -> 0.02/5 * 1000 = 5mL
Therefore, 25mL-5mL must be made isotonic (20mL)
Therefore 1.026/5 = 0.2052g * 1000 =205mg of Boric Acid must be added.
Apparently however, this is wrong! Could someone please point out my error?
Many thanks!