Pharmacy Calculations

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Pharmacy Calculations

Postby CreekNation85 » Sat Jul 09, 2011 5:49 am

hello, I am new to this. I am studying for my PTCB and have come accross a question that has really got me stumped for some reason. I wondering if anyone could shed some light for me. What is the answer and or steps to determine the answer.Any help would be greatly apreciated. Thank you. :?:

How many milliliters of active ingredient are contained in a pint of 15% v/v solution?

Re: Pharmacy Calculations

Postby Guest » Mon Jan 09, 2012 6:42 am

Lab experiments and types of research often require preparation of chemical solutions in their procedure. We look at preparation of these chemical solutions by weight (w/v) and by volume (v/v).

Using percentage by volume (v/v) When the solute is a liquid, it is sometimes convenient to express the solution concentration as a volume percent.

The formula for volume percent (v/v) is: [Volume of solute (ml) / Volume of solution (ml)] x 100

ex. Make 1000ml of a 5% by volume solution of ethylene glycol in water.
First, express the percent of solute as a decimal: 5% = 0.05
Multiply this decimal by the total volume: 0.05 x 1000ml = 50ml (ethylene glycol needed).

Subtract the volume of solute (ethylene glycol) from the total solution volume:
1000ml (total solution volume) - 50ml (ethylene glycol volume) = 950ml (water needed)

Dissolve 50ml ethylene glycol in a little less than 950ml of water. Now bring final volume of solution up to 1000ml with the addition of more water. (This eliminates any error because the final volume of the solution may not equal the calculated sum of the individual components).

So, 50ml ethylene glycol / 1000ml solution x100 = 5% (v/v) ethylene glycol solution.

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