Q: A patient weighs 180 lb. What is the patient's mass in kilograms? (1 kg = 2.20 lb)

$$180 \div 2.20 = 81.8\ \text{kg}$$

Q: A rattlesnake is 2.44 meters long. How many centimeters long is the snake? (1 m = 100 cm)

$$2.44 \times 100 = 244\ \text{cm}$$

Q: A doctor's order prescribes 0.200 mg of a medication. If each tablet contains 50 mcg, how many tablets are needed? (1 mg = 1000 mcg)

$$0.200\ \text{mg} \times \frac{1000\ \text{mcg}}{1\ \text{mg}} \times \frac{1\ \text{tablet}}{50\ \text{mcg}} = 4\ \text{tablets}$$

Q: How many minutes are in 1.4 days?

$$1.4 \times 24 \times 60 = 2016\ \text{minutes}$$

Q: If your pace on a treadmill is 65 meters per minute, how many minutes will it take to walk 3.9 kilometers?

$$3.9\ \text{km} \times \frac{1000\ \text{m}}{1\ \text{km}} \div 65\ \text{m/min} = 60\ \text{minutes}$$

Q: A solution contains 250 mg of a drug. How many micrograms (mcg) does this represent? (1 mg = 1000 mcg)

$$250 \times 1000 = 250,000\ \text{mcg}$$

Q: The $$LD_{50} of $$caffeine is $$192\ \text{mg/kg}. $$What does this value mean?

A dose of $$192\ \text{mg}$$ per kilogram of body mass is lethal to 50% of test animals.

Question 1

A patient weighs 180 lb. What is the patient's mass in kilograms? (1 kg = 2.20 lb)

Accepted Answer

$$180 \div 2.20 = 81.8\ 	ext{kg}$$

Question 2

A rattlesnake is 2.44 meters long. How many centimeters long is the snake? (1 m = 100 cm)

Accepted Answer

$$2.44 	imes 100 = 244\ 	ext{cm}$$

Question 3

A doctor's order prescribes 0.200 mg of a medication. If each tablet contains 50 mcg, how many tablets are needed? (1 mg = 1000 mcg)

Accepted Answer

$$0.200\ 	ext{mg} 	imes \frac{1000\ 	ext{mcg}}{1\ 	ext{mg}} 	imes \frac{1\ 	ext{tablet}}{50\ 	ext{mcg}} = 4\ 	ext{tablets}$$

Question 4

How many minutes are in 1.4 days?

Accepted Answer

$$1.4 	imes 24 	imes 60 = 2016\ 	ext{minutes}$$

Question 5

If your pace on a treadmill is 65 meters per minute, how many minutes will it take to walk 3.9 kilometers?

Accepted Answer

$$3.9\ 	ext{km} 	imes \frac{1000\ 	ext{m}}{1\ 	ext{km}} \div 65\ 	ext{m/min} = 60\ 	ext{minutes}$$

Question 6

Which of the following best describes the purpose of using conversion factors in chemistry?

Accepted Answer

To change a measurement from one unit to another using known relationships.

Question 7

A solution contains 250 mg of a drug. How many micrograms (mcg) does this represent? (1 mg = 1000 mcg)

Accepted Answer

$$250 	imes 1000 = 250,000\ 	ext{mcg}$$

Question 8

Which of the following is the correct sequence of steps for solving a unit conversion problem?

Accepted Answer

Identify given units, determine needed units, find conversion factors, set up and solve.

Question 9

A toxicologist is comparing the toxicity of two substances. Substance A has an $$LD_{50} of$$ $$3\ 	ext{mg/kg}$$, and Substance B has an $$LD_{50} of$$ $$300\ 	ext{mg/kg}. $$Which statement is correct?

Accepted Answer

Substance A is more toxic than Substance B.

Question 10

The $$LD_{50} of $$caffeine is $$192\ 	ext{mg/kg}. $$What does this value mean?

Accepted Answer

A dose of $$192\ 	ext{mg}$$ per kilogram of body mass is lethal to 50% of test animals.

Question 11

A nurse needs to administer 0.5 g of a medication. The tablets available are 250 mg each. How many tablets should be given? (1 g = 1000 mg)

Accepted Answer

$$0.5\ 	ext{g} 	imes \frac{1000\ 	ext{mg}}{1\ 	ext{g}} \div 250\ 	ext{mg} = 2\ 	ext{tablets}$$

Question 12

Which of the following statements about $$LD_{50} is $$TRUE?

Accepted Answer

$$LD_{50} is $$the dose that kills 50% of a test population.

Question 13

A medication is prescribed at 0.75 mg/kg for a 60 kg patient. How many milligrams should be administered?

Accepted Answer

$$0.75\ 	ext{mg/kg} 	imes 60\ 	ext{kg} = 45\ 	ext{mg}$$

Question 14

Which of the following is a correct example of a conversion factor?

Accepted Answer

$$\frac{1\ 	ext{kg}}{2.20\ 	ext{lb}}$$

Question 15

A laboratory animal receives a dose of 0.025 g of a substance. If the animal weighs 500 g, what is the dose in mg/kg?

Accepted Answer

$$0.025\ 	ext{g} 	imes \frac{1000\ 	ext{mg}}{1\ 	ext{g}} \div 0.5\ 	ext{kg} = 50\ 	ext{mg/kg}$$

Question 16

Which of the following best explains why multiple conversion factors are sometimes needed in a calculation?

Accepted Answer

Because the given and needed units may not be directly related, requiring intermediate steps.

Question 17

A patient is prescribed 0.3 mg of a drug. The available tablets are 100 mcg each. How many tablets are needed? (1 mg = 1000 mcg)

Accepted Answer

$$0.3\ 	ext{mg} 	imes \frac{1000\ 	ext{mcg}}{1\ 	ext{mg}} \div 100\ 	ext{mcg} = 3\ 	ext{tablets}$$

Question 18

Which statement best summarizes Paracelsus's principle in toxicology?

Accepted Answer

The dose determines whether a substance is a poison or a cure.

Chemistry and Measurements: Unit Conversions and Toxicology

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