titration

[nickelbackfan]

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If 25.0 mL of sulfuric acid solution (.1M) requires the addition of 23.0 mL of the barium hydroxide titrant solution to reach zero current, then the concentration of the barium hydroxide solution must be:

A. less than 0.050 M.
B. greater than 0.050 M, but less than 0.10 M.
C. greater than 0.10 M, but less than 0.150 M.
D. greater than 0.150 M.

answer is

C

I chose B. I was wondering why you dont add the volumes? My calculation was like 25(.1)=48(x)

 

[richkaj]

It is a equilibrium question. MV=MV... Knowing they are proportional a decrease in volume would lead to a increase in concentration... They must equal the same on each side...

 

[LoLCareerGoals]

I picked C for reason above, but I am a bit thrown off by "to reach zero current". What current?
Is this a galv. battery? do we need to invoke emf equation somehow to see that to reach zero current is to have equal moles of acid/base?

 

[Tenebrus]

I'm not sure why you would add them. This in comparing titration of a strong acid with a strong base, you have to compare the moles added of each, so since there were 2(.1 M)(.025 L) of protons (2 since its H2SO4), you would need to set that equal to 2(x M)(.023 L) of hydroxide from Ba(OH2) and solve for x...

EDIT: Assuming you were using M1V1=M2V2, you would only add when you're conisidering the same species, like H2SO4 and HNO3 for example.

 

[nickelbackfan]

I'm not sure why you would add them. This in comparing titration of a strong acid with a strong base, you have to compare the moles added of each, so since there were 2(.1 M)(.025 L) of protons (2 since its H2SO4), you would need to set that equal to 2(x M)(.023 L) of hydroxide from Ba(OH2) and solve for x...

EDIT: Assuming you were using M1V1=M2V2, you would only add when you're conisidering the same species, like H2SO4 and HNO3 for example.

by same species do you mean strong acid + strong acid?

Also this is from a passage, you can ignore the current part. It isnt a electro chemical cell

 

[richkaj]

I believe that is correct. For instance the concentration of a particular species due to the common ion effect. Hopefully the MCAT doesn't get too detailed for this but I could be wrong it is the MCAT...