Answer:
0.200 M NaOH: 13.3 mL of the concentrated solution and complete to 20.0mL
0.150 M NaOH: 10.0 mL of the concentrated solution and complete to 20.0mL
0.100 M NaOH: 6.67 mL of the concentrated solution and complete to 20.0mL
0.050 M NaOH: 3.33 mL of the concentrated solution and complete to 20.0mL
0.025 M NaOH: 1.67 mL of the concentrated solution and complete to 20.0mL
Explanation:
It is possible to prepare a solution from a more concentrated one. In the problem, the concentrated solution is 0.300M NaOH. Thus, to prepare 20.0mL of each of the solutions you will need:
0.200 M NaOH: 20.0mL × (0.200M / 0.300M) = 13.3 mL of the concentrated solution and complete to 20.0mL
The ratio between the concentrated solution and the solution you want to prepare is called "dilution factor"
0.150 M NaOH: 20.0mL × (0.150M / 0.300M) = 10.0 mL of the concentrated solution and complete to 20.0mL
0.100 M NaOH: 20.0mL × (0.100M / 0.300M) = 6.67 mL of the concentrated solution and complete to 20.0mL
0.050 M NaOH: 20.0mL × (0.050M / 0.300M) = 3.33 mL of the concentrated solution and complete to 20.0mL
0.025 M NaOH: 20.0mL × (0.025M / 0.300M) = 1.67 mL of the concentrated solution and complete to 20.0mL