(11) Example problem: How many grams of potassium permanganate

(KMnO4) are needed to make this prescription?

(a) Before beginning the calculation, the prescription must be analyzed

to see exactly what the physician wants. The prescription states that the pharmacist

should dispense a solution of potassium permanganate in distilled water. The solution

should have a strength equivalent to 1 gram per 5000 milliliters and the pharmacist

should dispense 120 milliliters of the solution. The expression of strength will be the

first ratio of the proportion:

1 gram =

_______________

5000 ml

(b) Assign the X value:

1 gram

=

X gram__

5000 ml

(c) Find the other known factor:

1 gram

=

X gram___

5000 ml

120 ml

(d) Then, cross-multiply:

5000 (x)

=

1 (120)

5000 x

=

120

(e) Solve for X:

X

=

120

5000

X

=

0.024

(f) Refer to the proportion for the units of X:

X

=

0.024 gram

MD0802

1-39

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