Acid-base equilibrium question titration

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Discussion Overview

The discussion revolves around various acid-base equilibrium problems, specifically focusing on titration calculations and buffer solution pH determination. Participants are attempting to solve homework problems related to these topics and are seeking clarification on their methods and results.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant calculates the concentration of NaOH using the moles of potassium hydrogen phthalate but arrives at a different answer than expected, prompting a request for help.
  • Another participant suggests that the discrepancy in the NaOH concentration might be due to rounding errors in intermediate calculations.
  • A new question is posed regarding the pH of a buffer solution made from KIO3 and HIO3, with the participant expressing confusion about how to approach the problem without specific volumes.
  • Concerns are raised about the incorrect setup of the ICE table for the buffer solution, noting that KIO3 is fully dissociated and should not be treated as having an initial concentration of zero.
  • A participant presents another titration problem involving H3PO4 and calcium hydroxide, detailing their calculations but questioning their accuracy based on the provided answer.
  • Responses highlight the importance of not rounding intermediate results and maintaining proper notation in chemical formulas.
  • One participant acknowledges resolving their confusion but does not specify how they did so.

Areas of Agreement / Disagreement

Participants express differing views on the accuracy of calculations and the proper approach to solving the problems. There is no consensus on the correct methods or answers, and some participants challenge each other's reasoning.

Contextual Notes

Some calculations depend on assumptions about the stoichiometry of reactions and the completeness of dissociation, which are not fully detailed in the posts. Additionally, the lack of specific volumes in some questions limits the ability to arrive at definitive answers.

Who May Find This Useful

Students studying acid-base chemistry, particularly those working on titration problems and buffer solutions, may find this discussion relevant.

Nelo
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Homework Statement



6.83 mL of a solution of NaOH is standardized against 3.06 g of potassium hydrogen phthlate
(KHC8O4H4). Calculate the concentration of the base.

Homework Equations



c=n/v
M of KHP = 198.201




The Attempt at a Solution



Here is what I did.
Calculated moles of pottassium hydrogen phthalate

3.06/198.201 = 0.0154 mol.
Used the volume of naoh to calculate concentration.

c=n/v . c= 0.0154/ 0.00683

c= 2.25 mol/L

The answer is 2.15. What have i done wrong?
 
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Must be mistake in the key.

But the answer is not 2.25, it is 2.26. Don't round down intermediate values.
 
I have another question here.

"Calculate the pH of a buffer solution made by mixing 0.14 M KIO3 and 0.18 M HIO3"

The question is so vague, I have no idea where to start. All i know is that the ka of hio3 is 0.170 *from google*... and the ice table.



My attempt: assuming its a neutrilization i did Mhio3 - Mkio3 = 0.04 .

so hio3 remains.

Hio3 + h2o ----> -ion h3o+

0.04-x / x x


Ka being 0.170 = x^2/0.04-x

Since the 500 rule doesn't work, I did the quadratic formula.

Giving me -x2 + 6.8*10^-3 -0.170x ( -x^2 -0.170x +6.8*10^-3)

Used the formula.

calculating 0.0334 M

-log of that is 1.47. however the answer is 0.66

What have i done wrong?
 
Without volumes (or at least their ratio) given question can't be answered.

Regardless of whether the question can be answered or not, your ICE table is wrong. KIO3 is fully dissociated, which means initial concentration of IO3- is not zero.

Please use correct capitalization, things like hio3 or -ion don't mean anything.
 
Well, ... what about this one? ( I am doing exam review questions, no ka charts or any of the such are really given , theyre pretty awful. Sorry if I am being annoying, I just want to know how to do all of these)

Quest. : "What volume of 0.765 M H3PO4 is required to exactly neutralize 2.000 g of calcium hydroxide?"

My attempt: 2g of caoh / 57.084 = 0.0350mol of caoh.

used stoic (balanced eq. was not given) 2h3po4 + 3caoh -----> Ca3(PO4)2 + 6h2o

2/3 * 0.0350 = 0.02333mol of h3p04.

V= n/c 0.02333/0.765 = 0.0304L. Which is wrong. The ansswer is.. : 0.0235.

Notice anything wrong?
 
Nelo said:
Notice anything wrong?

At least two things.

First, with each new post you ignore earlier comments. Yesterday I told you to not round down intermediate results, today you started with the same mistake. 10 minutes ago I told you to use correct capitalization of formulas, now you write things like caoh. If you are seriously thinking bout getting help, don't ignore it, or you will be not treated seriously.

Second, caoh is wrong not only because of incorrect capitalization.
 
Thanks, figured it out
 

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