Answer:
The concentration of silver nitrate in solution #4 is 4.781 × 10⁻⁷ M.
Step-by-step explanation:
Let´s express the initial concentration in cientific notation:
0.0003321 M = 3.321 × 10⁻⁴ M
In the first dilution step, the student takes 5 ml and add water to 50 ml. The dilution factor is 5 ml/50 ml = 1/10. It means that the concentration is reduced ten times. Then, after the first step the concentration of the solution will be:
3.321 × 10⁻⁴ M · 1/10 = 3.321 × 10⁻⁵ M (concentration of solution #2)
In the next step, the solution is diluted by 10 ml /250 ml = 1/25. Then, the solution will be diluted 25 times. The concentration of solution #3 is:
3.321 × 10⁻⁵ M · 1/25 = 1.328 × 10⁻⁶ M
Finally, the dilution factor will be 18 ml / 50 ml = 9/25. Then, the concentration of solution #4 will be:
1.328 × 10⁻⁶ M · 9/25 = 4.781 × 10⁻⁷ M
The concentration of silver nitrate in solution #4 is 4.781 × 10⁻⁷ M.
Attached you will find a figure that illustrates what amount of the original solution is present in each diluted solution. In the first dilution, there are 5 ml of the original solution in the 50 ml solution. In the second dilution, the volume of the original solution is 1 ml in the 250 ml of solution #3. In solution #4, the volume from the original solution is 0.072 ml.
The solution #4 could be prepared taking 0.072 ml from the original solution and adding water to 50 ml, but it wouldn´t be a good practice.