Final answer:
To solve for the amount of 60% copper sulfate solution needed to make a 30% solution, we use dilution calculation. However, the exact answer of 6.67 mL doesn't match the provided options, suggesting an approximation is expected, and 10 mL is the closest option.
Step-by-step explanation:
The student is attempting to create a mixture of solutions to achieve a desired concentration of copper sulfate. To solve this, we can use the concept of dilution and the conservation of mass of the solute (copper sulfate) in the solution. We start by finding out how much copper sulfate is in the 25% solution. Then we calculate the amount of copper sulfate in the desired 30% solution. Finally, we determine how much of a 60% solution is needed to reach that final concentration.
First, let's set up the equation representing the mass of copper sulfate before and after the addition:
(Volume of 25% solution) × (Concentration of 25% solution) + (Volume of 60% solution) × (Concentration of 60% solution) = (Total Volume) × (Desired Concentration)
Converting percentages to decimal form for the computation gives us this equation:
40 mL × 0.25 + x mL × 0.60 = (40 mL + x mL) × 0.30
Now, let's solve for x (the volume of the 60% solution needed):
- 10 mL + 0.6x = 12 mL + 0.3x
- 0.3x = 2 mL
- x = 2 mL / 0.3
- x = 6.67 mL
However, this answer is not one of the multiple-choice options given, indicating a potential error in the question options, a misunderstanding of the question, or an approximation is expected for the answer.
Typically, when solving these problems, one of the options should closely match the calculated answer. Due to the nature the options given and typical rounding in chemistry, the student might be expected to choose the closest option, which in this case would be option (a) 10 mL, acknowledging that this is an approximation.