1. In order to make 250mL of a 0.100 M HNO3 solution from a 15.9 M stock solution, then _____mL if the 15.9 M stock HNO3 solution is needed.
M1V2=M2V2, solve for V2.
(0.100M * 250mL)/ 15.9M = 1.6mL
V2-V1=V
1.6mL-250= -248.4
Did I do this correctly?
Two picky points here.
1. You have 3 significant figures in 0.100 and three in 15.9 (and I'm calling 250 3 although some would call that only two since there is no decimal after the zero) so I would keep 3 in the answer and not round it to 1.6 (that is about 1.57 or so).
2. The question asks for mL of the 15.9M solution which you answered. You gave additional information about the amount of water to add to make up the 150 mL. However, fluids are not additive although at this concn I don't think there will be any difference but I always say, "Add 1.67 of the stock solution to a 250 mL volumetric flask and add distilled water to the mark of the volumetric flask." That may or may not be 248.4 mL but you really don't care how much H2O it is. If you follow those directions you will ALWAYS have the right concentration and it makes no difference, if done this way, if the volume of the two solutions are or are not additive.
It appears that there are a couple of errors in your calculations. Let's go through the steps correctly to find the answer.
First, we have the formula M1V1 = M2V2, where M1 is the initial concentration, V1 is the initial volume, M2 is the final concentration, and V2 is the final volume.
In this case, we want to make a 250 mL solution of 0.100 M HNO3 from a 15.9 M stock solution. So, we have:
M1 = 15.9 M (concentration of the stock solution)
V1 = ? (unknown initial volume)
M2 = 0.100 M (desired concentration)
V2 = 250 mL (final volume)
We need to solve for V1. Rearranging the formula, we have:
V1 = (M2 * V2) / M1
Plugging in the given values, we get:
V1 = (0.100 M * 250 mL) / 15.9 M
V1 ≈ 1.57 mL
So, approximately 1.57 mL of the 15.9 M stock HNO3 solution is needed to make a 250 mL solution with a concentration of 0.100 M.
To summarize, you made a mistake in your calculation. The correct answer is approximately 1.57 mL, not 1.6 mL.