SAT Chemistry practice from College Board
The hydrogen ion concentration of a solution prepared by diluting 50. mL of 0.10 M HNO3(aq) with water to 500. mL of solution is
(A) 0.0010 M
(B) 0.0050 M
(C) 0.010 M
(D) 0.050 M
(E) 1.0 M
Answer and Explanation:
One of the key words in this question is diluting. A solution gets diluted when more water is added and thus the concentration decreases. The formula for dilution is M1V1=M2V2 where M stands for molarity and V stands for volume. Volume can have any units as long as both sides are consistent. We should also realize that HNO3 is a strong acid. Strong acids dissociate completely, and therefore the molarity of the strong acid equals the hydrogen ion concentration. Let's use our formula first to calculate the new concentration of the acid.
0.10M (50ml) = M2 (500ml)
The new concentration of the acid id 0.001M. Since this is a strong acid, this also equals the hydrogen ion concentration. Therefore, choice A is the correct answer choice.
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