Assistant Laboratory Animal Technician (ALAT) Practice Exam

You are preparing a 1:4 dilution of substance A. If the final volume is 400 mL, what is the volume of substance A you need?

1. 50 mL

2. 100 mL

3. 200 mL

4. 300 mL

The correct answer is: 100 mL

To determine the volume of substance A needed for a 1:4 dilution where the final volume is 400 mL, it's essential to understand what a 1:4 dilution means. This dilution ratio indicates that for every 1 part of substance A, there are 4 parts of total dilution, which means substance A is mixed with 3 parts of diluent (like water or another solvent). In practical terms, if we consider the total parts in this dilution, we have 1 part of substance A plus 4 parts total (1 part A + 3 parts diluent), which equals 5 total parts. To find the volume of the parts that correspond to substance A, we can set up the ratio. Calculating the volume of substance A involves finding the fraction of the total volume that corresponds to its part in the dilution. Since we have a final total volume of 400 mL, we can find the volume of substance A by taking 1 part out of the total 5 parts: Volume of substance A = (1 part / 5 parts) × 400 mL = 80 mL. However, recognizing a possible misunderstanding in the given answer choices, the calculation aligns with a standard dilution approach but should