• Funniest Story on the Job Contest Starts Now!

    Contest starts now and ends September 27th. Winner will receive a special user banner and $10 Amazon Gift card!

    JOIN NOW
  • Site Updates Coming Next Week

    Site updates are coming next week on Monday and Friday. Click the button below to learn more!

    LEARN MORE

AAMC Chem Qpack #49 explanation.

Antiseptic11

Full Member
2+ Year Member
Mar 26, 2017
77
143
136
  1. Pre-Medical
When 2.0 mL of 0.1 M NaOH(aq) is added to 100 mL of a solution containing 0.1 M HClO(aq) and 0.1 M NaClO(aq), what type of change in the pH of the solution takes place?

Screen Shot 2020-06-23 at 10.11.33 PM.png

Hey ya'll, so the answer here is A. I do understand the "intuitive" way of answering this (which is the basis of the AAMC explanation) but I've been working on this for hours and cannot figure out how to do it the long way. I know it's unlikely for us to come across long calculations but I really just want to make sure that I at least know the foundation. I saw this post on reddit, but I couldn't follow what they did after they've calculated the moles of the acid & the base. I would really appreciate if someone could walk me through this.

Thank you!!
 

robinson annulation

Full Member
2+ Year Member
Aug 20, 2017
394
512
116
somewhere
  1. Medical Student
in order to do it the long way, we would need the pKa value of HClO.

since the concentration of the weak acid and conjugate base are equal, the initial pH of the buffer soln = the pKa of HClO.

steps for the "long way":
1. figure out the amount of moles of NaOH, HClO, and NaClO after NaOH is added (so total volume is 102 mL)
2. use the equation NaOH + HClO -> NaClO + H2O for your ice table
3. use the number of moles from step 1 for the ice table
4. you will be left w/ zero moles of NaOH, a lower than initial amount of HClO, and a higher than initial amount of NaClO
5. use these numbers, along w/ the pKa, for the Henderson-Hasselbalch equation to figure out the new pH
6. compare this new pH to the initial pH (which was the pKa)
 
  • Like
Reactions: 1 user

Antiseptic11

Full Member
2+ Year Member
Mar 26, 2017
77
143
136
  1. Pre-Medical
in order to do it the long way, we would need the pKa value of HClO.

since the concentration of the weak acid and conjugate base are equal, the initial pH of the buffer soln = the pKa of HClO.

steps for the "long way":
1. figure out the amount of moles of NaOH, HClO, and NaClO after NaOH is added (so total volume is 102 mL)
2. use the equation NaOH + HClO -> NaClO + H2O for your ice table
3. use the number of moles from step 1 for the ice table
4. you will be left w/ zero moles of NaOH, a lower than initial amount of HClO, and a higher than initial amount of NaClO
5. use these numbers, along w/ the pKa, for the Henderson-Hasselbalch equation to figure out the new pH
6. compare this new pH to the initial pH (which was the pKa)

Thank you!!!
 
This thread is more than 1 year old.

Your message may be considered spam for the following reasons:

  1. Your new thread title is very short, and likely is unhelpful.
  2. Your reply is very short and likely does not add anything to the thread.
  3. Your reply is very long and likely does not add anything to the thread.
  4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
  5. Your message is mostly quotes or spoilers.
  6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
  7. This thread is locked.