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Rx: Castor oil 10% (v/v) Tween 80 and Span 20 2% (w/v) Simple syrup qs 50...

Rx:
Castor oil	10% (v/v)
Tween 80 and Span 20	2% (w/v)
Simple syrup	qs 50 mL

How many gram(s) of Span 20 are needed to prepare for the prescription, given that the required HLB for the emulsion is 10, Span 20 has an HLB of 8.6, and Tween 80 has an HLB of 15?

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Expert Solution

Solution :

HLB means Hydrophilic - Lipophilic Balance.HLB scale range from 0 to 20.

Most important aspect of HLB system is that HLB values are additive if the amount of each in a blend is taken into account. Thus blends of high and low HLB surfactants can be used to obtain the required HLB of an oil.

Span has lipophilic properties and have low HLB value of 1.8 - 8.6. here Span 20 HLB value is 8.6

Tween has hydrophilic properties , it is Polyoxyethylene derivative of span. it has high HLB vlue is 9.6 - 16.7 . Tween 80 HLB value is 15.

Assume Tween 80 (HLB 15 ) is A and Span 20 (HLB 8.6) is B

The perecentage equation form is A = 100 ( X - HLB_B ) ( HLB_A - HLB_B )

B = 100 - A

Where X = required HLB value of the emulsion = 10

HLB_A = HLB value of Tween 80 = 15

HLB_B = HLB value of Span 20 = 8.6

Mixture of Tween 80 and Span 20 weight is 2grams.

Equation is A = 100 ( X - HLB_B ) ( HLB_A - HLB_B )

= 100 ( 10 - 8.6) ( 15 - 8.6)

= 100 ( 1.4) ( 6.4)

= 140 6.4

A = 21.8%

B = 100 - A

= 100 - 21.8

B = 78.2%

Weight of tween 80 (A) and Span 20 is needed to form emulsion with HLB 10 are calculated by

Weight of tween 80 (A) = percentage of A weight of mixture 100

= 21.8 2 100

= 43.6 100

Weight of tween 80 (A) = 0.436 grams

Weight of Span 20 (B) = weight of mixture - Weight of tween 80 (A)

= 2 - 0.436

Weight of Span 20 (B) = 1.564 grams

1.564 gms of Span 20 is needed to prepare for the prescription,given that the required HLB for the emulsion is 10.

Nightingale answered 1 year ago

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