Module 3.1: Pharmaceutical Calculation Pretest

Explanation
To obtain 50 units of insulin, 0.5 mL of U-100 insulin should be used. U-100 insulin means that there are 100 units of insulin in 1 mL. Therefore, to get 50 units, half a milliliter (0.5 mL) of U-100 insulin is required.

Explanation
If 20 mL contains 60 doses, then each dose is 20 mL / 60 doses = 1/3 mL. Since the dropper calibrates 35 gtts per mL, the number of drops in each dose would be 1/3 mL * 35 gtts/mL = 35/3 ≈ 11.67 gtts. Since we can't have a fraction of a drop, the closest whole number is 12 gtts, which would be prescribed in each dose of the liquid medicine.

Explanation
To find the total amount of the drug needed, we need to multiply the number of dosage forms (74) by the amount of the drug in each form (1/10 grain).

First, we convert 1/10 grain to milligrams. There are 64.8 milligrams in 1 grain, so 1/10 grain is equal to 6.48 milligrams.

Next, we multiply the amount of the drug per form (6.48 mg) by the number of forms (74): 6.48 mg * 74 = 479.52 mg.

Since we cannot have a fraction of a milligram, we round up to the nearest whole number, which is 480 mg.

Therefore, the correct answer is b. 480 mg.

Explanation
The specific gravity of a liquid is the ratio of its density to the density of water. In this question, the weight of the liquid is given in grains, which is a unit of mass. To find the specific gravity, we need to convert the weight to mass by dividing it by the acceleration due to gravity. Then, we divide the mass by the density of water to find the specific gravity. Since the specific gravity is less than 1, it means that the liquid is less dense than water. Therefore, the correct answer is d. 1.26.

Explanation
To calculate the grams of dextrose required, we need to multiply the volume of the solution (4500 L) by the percentage concentration (5%).

First, we convert the percentage to a decimal by dividing it by 100: 5/100 = 0.05.

Then, we multiply the volume (4500 L) by the concentration (0.05): 4500 L * 0.05 = 225 g.

Therefore, 225,000 g of dextrose are required to prepare 4500 L of a 5% solution.

Explanation
To make a 5% (w/w) solution, 5 grams of the drug substance should be dissolved in 100 mL of water. Therefore, to find the amount of drug substance needed for 250 mL of water, we can set up a proportion: 5 grams/100 mL = x grams/250 mL. Solving for x gives us x = (5 grams/100 mL) * 250 mL = 12.5 grams. Since the answer choices are given in grams, we round up to the nearest gram, which is 13 grams. Therefore, the correct answer is 13.16 g.

Explanation
To convert a percentage to mg/mL, you need to multiply the percentage by 10. Since 5% multiplied by 10 equals 50, the correct answer is a. 50 mg/mL.

Explanation
To make a 70% alcohol solution, equal parts of alcohols with 90% and 50% strengths need to be mixed. This is because the average of the two strengths (90% + 50%) / 2 = 70%. Therefore, the correct proportion is 1 part of 90% alcohol to 1 part of 50% alcohol.

Explanation
To prepare a liquid with a specific gravity of 0.925, we need to mix two liquids with different specific gravities. The specific gravity of a liquid is the ratio of its density to the density of water.

To find the amount of each liquid needed, we can use the formula:

(volume of liquid 1 x specific gravity of liquid 1) + (volume of liquid 2 x specific gravity of liquid 2) = (total volume of mixture x specific gravity of mixture)

Let's assume the volume of liquid 1 is x mL and the volume of liquid 2 is y mL.

0.950x + 0.875y = 0.925 * 1500

Solving this equation, we get x = 1000 mL and y = 500 mL.

Therefore, the correct answer is a. 1000 mL (sp gr 0.950) 500 mL (sp gr 0.875).

Explanation
Zinc chloride is a three-ion electrolyte, meaning it dissociates into three ions when it is in solution. The question states that it dissociates 80% in a certain concentration. The dissociation factor (I) is calculated by dividing the actual dissociation by the theoretical dissociation. In this case, the theoretical dissociation is 100% since it is a three-ion electrolyte. Therefore, the dissociation factor is 80%/100% = 0.8. To convert this to a whole number, we can multiply by 10, giving us 8. To convert this to a decimal, we divide by 3, giving us 2.6. Therefore, the correct answer is a. 2.6.