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Determining W/W and W/V of solutions:
One gram of boric acid is soluble in 18 ml of water and makes a saturated solution.
What is the percentage w/w and w/v of a saturated sol of boric acid?
Step1. calculate the total weight of the solution:
1ml of water weight 1g
a////1g + 18g =19g////a

Step 2. calculate the percentage w/w of the sol. By setting up a proportion between the weights and the percentages of saturation:
a////19g / 1g=100%/x(%w/w of sol.)////a
a////x= 5.26% w/w, answer.////a

Step 3. because the volume of the solution is between 18 and 19ml, we know the w/v concentration is greater than 5.26% . assume the volume is 18.2 ml, and calculate the w/v conc.
a////1g / 18.2ml=x(%w/v) / 100%////a
x= 5.5% w/v , answer.


Determining quantity of active drug:
A pharmacist receives a prescription for 8 oz of an oral rinse to contain 10 ppm fluoride ion (F-) in orange flower water. How much sodium fluoride (NaF) would be required to prepare this compound?

Step 1. convert ounces to milliliters (1 oz = 29.57 ml) and calculate the total volume of the sol.
a////8 X 29.57 = 237 ml////a

Step 2. convert parts per million (ppm) to a ratio concentration and set up the following proportion to calculate the quantity of fluoride ion required for the prescription:
a////10g / 1000000 ml = x / 237 ml////a
x = 0.0024 g =2.4mg of F-, answer.

Step 3. given that 1 mg F-=2.2mg NaF, calculate the quantity of NaF required:
a////1mg F-/2.2mg NaF= 2.4mg F-/x(mg NaF)////a

a////x = 5.3mg NaF////a
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