How to prepare a 500ml 0.2M NaOH solution from 2.0M NaOH solution
2 answers
you want 1/10 the concentration, so you will need 10 times the volume.
I think the question here hinges on HOW to prepare. There are two steps.
1. Determine how much of the 2.0 M NaOH to use. I use
c1v1 = c2v2 where
c = concn
v = volume
2.0*v1 = 0.1*500
v1 = 50 mL of the 2.0M solution.
Step 2. Here is where many students miss it. They will answer, "Mix 50 mL of the 2.0M NaOH and add 495 mL H2O to make a total of 500 mL." But that assumes the volumes are additive. The correct answer is
"Pipet 50. mL of the 2.0 M NaOH into a 500 mL volumetric flask, add water to the mark on the volumetric flask and mix thoroughly." Note that you may have added "very close" to 495 mL H2O but not that exact amount.
1. Determine how much of the 2.0 M NaOH to use. I use
c1v1 = c2v2 where
c = concn
v = volume
2.0*v1 = 0.1*500
v1 = 50 mL of the 2.0M solution.
Step 2. Here is where many students miss it. They will answer, "Mix 50 mL of the 2.0M NaOH and add 495 mL H2O to make a total of 500 mL." But that assumes the volumes are additive. The correct answer is
"Pipet 50. mL of the 2.0 M NaOH into a 500 mL volumetric flask, add water to the mark on the volumetric flask and mix thoroughly." Note that you may have added "very close" to 495 mL H2O but not that exact amount.
5 answers