Question

In order to prepare very dilute solutions, a lab technician chooses to perform a series of dilutions instead of measuring a very small mass. A solution was prepared by dissolving 0.360 g of KNO3 in enough water to make 500. mL of solution. A 10.0 mL sample of this solution was transferred to a 500.0-mL volumetric flask and diluted to the mark with water. Then 10.0 mL of the diluted solution was transferred to a 250.0-mL flask and diluted to the mark with water. What is the final concentration of the KNO3 solution?

7.91 × 10-9 M
5.70 × 10-6 M
2.85 × 10-6 M
7.12 × 10-3 M
1.42 × 10-4 M

Answer 1

5.70*10-6 M

Step-by-step explanation:

Convert grams of KNO3 to moles. 0.360 g = 0.00356 mol

Convert moles to molarity by dividing moles by the volume.

• Dilution 1: 0.00712 M
• Dilution 2: 1.42*10-4 M
• Dilution 3: 5.70*10-6 M

To get the second dilution, you must find the percentage of 10 mL to 500 mL. The percentage is 2%. The second dilution is 2% of 0.00712.

Do the same thing for dilution 3. The percentage of 10 mL to 250 mL is 4%. The third dilution is 4% of 1.42*10^-4.

Hope this helps! <3