titration question

[nickelbackfan]

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If it takes 1 gram of solid NaOH to change the pH of a solution containing a strong acid from 1 to 2, how much solid NaOH (in g) would be needed to change the pH of this solution from 2 to 3? Assume no volume change


answer


.1g



I'm not sure how they reached this. Can you use henderson hesselbach to solve it?

 

[indianjatt]

In order to go from a pH of 1 to a pH of 2, you need a change in concentration of 1/10 because the concentration of H+ at a pH of 1 is .1M. The concentration of H+ at a pH of 2 is .01M; so the concentration went down from .1M to .01M or a factor of 10. Going from pH 2 to a pH of 3, it is a change in concentration of .01M to a concentration of .001M. In this case it is also a change by a factor of 10.

So Basically we have this: the final Concentration at a pH of 2 is .01, while at a pH of 3 it's .001. Since molarity is moles/L, we need to have 1/10 the number of moles (or 1/10 the amount of grams) in order to go from a concentration of .01 to .001.

1g/10 = .1g or the amt to increase from a ph of 2 to 3.

 

[cloak25]

In order to go from a pH of 1 to a pH of 2, you need a change in concentration of 1/10 because the concentration of H+ at a pH of 1 is .1M. The concentration of H+ at a pH of 2 is .01M; so the concentration went down from .1M to .01M or a factor of 10. Going from pH 2 to a pH of 3, it is a change in concentration of .01M to a concentration of .001M. In this case it is also a change by a factor of 10.

So Basically we have this: the final Concentration at a pH of 2 is .01, while at a pH of 3 it's .001. Since molarity is moles/L, we need to have 1/10 the number of moles (or 1/10 the amount of grams) in order to go from a concentration of .01 to .001.

1g/10 = .1g or the amt to increase from a ph of 2 to 3.

Since going from pH 1 to pH 2 also differ by a factor of 10, shouldn't it also take 0.1g to go from pH 1 to pH 2? So for your explanation in the second paragraph...can't you also say the same for going from pH 1 to 2? or vice versa: going from pH 1 to pH 2 takes 1g of NaOH so shouldn't going from pH 2 to 3 also take 1g? since it also differs by a factor of 10.....😕

 

[Singhp03]

Since going from pH 1 to pH 2 also differ by a factor of 10, shouldn't it also take 0.1g to go from pH 1 to pH 2? So for your explanation in the second paragraph...can't you also say the same for going from pH 1 to 2? or vice versa: going from pH 1 to pH 2 takes 1g of NaOH so shouldn't going from pH 2 to 3 also take 1g? since it also differs by a factor of 10.....😕

no relative concentrations of [H] to volume(L) are not the same:
.1-->.01-->.001M

from this you could ask yourself, how would it take the same amount of NaOH to go from .1 to .01 as it does to go from .01 to .001? By estimation, ur answer should be less than 1g

 

[indianjatt]

I shouldn't been clear. I apologize. I just wanted to show that each pH increase was a factor of 1/10 and that did not change (hence some confusion), but what DID change were the absolute concentrations. and that alone told you that a pH of 3 has a concentration of .001M, which therefore has 1/10 the moles at a pH of 2.

 

[mehc012]

Alternatively, you could remember that pH is a log scale...therefore all things being equal, it should take 1/10 as much NaOH to go from 2-3 as it did to go from 1-2. This makes it a super quick question; simply divide the given amount by 10!