Here's a chemistry question. Could you help me?

Question

An infant acetaminophen suspension contains 80 mg/0.80 mL suspension. The recommended dose is 15 mg/kg body weight. How many mL of this suspension should be given to an infant weighing 14lb?

Answer 1

14 lb => 6.35 Kg

Mass needed = 6.35 Kg x 15 mg/Kg = 95.3 mg

Volume suspension = 0.80 mL x 95.3 mg / 80 mg =  0.953 mL

Answer 2

There are three steps (or conversions) required to answer this question. You start out by converting lbs to kgs, then you determine the number of mgs per kg, then finally the number of mls per mg.

I'll show you the long way and the short way ...

Step 1) Convert lbs to kgs

14lb  x   1 kg / 2.2 lb = 6.36 kg  (infant's weight in kg)

Step 2) Determine the dosage according to weight in kg

6.36 kg  x  15 mg / kg = 95.5 mg  (dose in mg for a 6.36 kg infant)

Step 3)Determine the number of mls req'd to deliver 95.5 mg

95.5 mg  x  0.80 ml / 80 mg = .955 (rounded to .96 ml)

You can also do all of the conversions in one long chain:

14 lb  x  1 kg /2.2 lb  x  15 mg/kg  x  0.80 ml/80 mg =  .955ml

   Notice that the unit in the numerator of factor #1 is in the denominator of factor #2, and the unit in the numerator of factor #2 is in the denominator of factor #3. These units cancel out step by step. First the lb cancel, then the kg cancel, then the mg cancel ... you know that you have set up your equations properly when the only unit that has not cancelled is the unit that you were asked for, and this unit should always be in the numerator. The first unit in the chain is always the unit that you were given to start (lb) and the last should be the unit that you were asked to find (mL).

   You will do these conversions all the time in chemistry.

I hope I helped, good luck!