2-9. EXAMPLE PROBLEMS
a. How many milliliters of a 2% stock solution of potassium permanganate
(KMn04) would be needed to compound the following prescription?
USE THESE STEPS:
Step 1: Write the formula.
V C = V1 C1
Step 2: Substitute values.
(X) (2%) = (120 ml) (.02%)
Step 3: Check units.
(a)
Units of concentration are both percent.
(b) X will have the same units as the volume
on the other side of the equal sign. In this case
"milliliters."
Step 4: Solve for X.
2 X = 2.4
X = 1.2 ml (answer)
NOTE: To compound the prescription: Obtain 1.2 milliliters of the 2% stock
solution of potassium permanganate, place it in a graduate, and "q.s." to 120
ml with distilled water.
b. How many grams of 14% zinc oxide ointment can be made from one pound
of 20% zinc oxide ointment?
USE THESE STEPS:
Step 1:
W C = W1 C1
Step 2 & 3: (X) (14%) = (454 g) (20%)
Step 4:
14 X = 9080 X = 648.57142 grams (answer) (can be rounded to
648.57 grams)
NOTE: The one lb was changed to 454 grams because the answer is to be grams.
MD0802
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