Ionic equilibrium titration

In summary: If neutralization means the two endpoints have the same pH, then the answer is 4g.The source of the question is a sample question for jee mains in India.
  • #1
Prabs3257
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4
Homework Statement
[" 50mL of "0.5M" Oxalic Acid is needed to neutralize "25mL" of sodium hydroxide "],[" solution.The amount of "NaOH" in "50mL" of the given sodium hydroxide solution is "]
Relevant Equations
Equation moles
I got a answer by equation the moles i took the n factor of oxalic acid as 2 and the naoh solution came out to be 2M but i got an answer of 4grams but the answer given is 2 grams am i correct ??
 

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  • #2
It's a bit ambiguous because there are two possible reactions:
OH- + 1/2 H2Ox → H2O + Ox2-
OH- + H2Ox → H2O + HOx-
I've written them that way because you are adding the oxalic acid to the NaOH (by the way, there's no such thing as naoh). You will first form disodium oxalate, then monosodium hydrogen oxalate. The titration will have two endpoints.
Can you estimate the pH at these endpoints? To make it a bit simpler, just try to calculate the pH of a 1M solution of Na2Ox, and a 1M solution of NaHOx. Which do you think best corresponds to "neutralisation" (if that term is not better defined in the problem)?
hint: for oxalic acid, pKa1 = 1.27, pKa2 = 4.27 (This question is assuming a lot of knowledge. How many marks do you get?)
 
  • #3
mjc123 said:
It's a bit ambiguous because there are two possible reactions:
OH- + 1/2 H2Ox → H2O + Ox2-
OH- + H2Ox → H2O + HOx-
I've written them that way because you are adding the oxalic acid to the NaOH (by the way, there's no such thing as naoh). You will first form disodium oxalate, then monosodium hydrogen oxalate. The titration will have two endpoints.
Can you estimate the pH at these endpoints? To make it a bit simpler, just try to calculate the pH of a 1M solution of Na2Ox, and a 1M solution of NaHOx. Which do you think best corresponds to "neutralisation" (if that term is not better defined in the problem)?
hint: for oxalic acid, pKa1 = 1.27, pKa2 = 4.27 (This question is assuming a lot of knowledge. How many marks do you get?)
this is a high school grade question but why can't we simply equate the milliequivallents of both oxalic acid and NaOH
 
  • #4
Titrations with oxalic acid are most usually done if I remember right by adding alkali to the acid, because you traditionally use as indicator phenolphthalein whose alkaline form is coloured (has pKa about 9) well above the oxalic acid pK's, so both -COOH groups have been titrated when you see the pink colour appear.

I get 4g; the student would have to set out reasoning in more detail for us to identify any misconception or mistake.
 
  • #5
epenguin said:
Titrations with oxalic acid are most usually done if I remember right by adding alkali to the acid, because you traditionally use as indicator phenolphthalein whose alkaline form is coloured (has pKa about 9) well above the oxalic acid pK's, so both -COOH groups have been titrated when you see the pink colour appear.

I get 4g; the student would have to set out reasoning in more detail for us to identify any misconception or mistake.
ya i am also getting 4g hence the answer given must be wrong thanks
 
  • #6
What is the source of the question?
 
  • #7
epenguin said:
What is the source of the question?
its a sample question for jee mains its an enterance exam in india
 
  • #8
Is 2g the official answer? I don't think I would be able to enter there.
However I hope we shall get a second opinion.
 
  • #9
Something is definitely wrong, 2 g is amount of NaOH that reacted, not amount of NaOH in 50 mL of the solution.
 
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  • #10
Which equivalence point? Are the two of them close-enough for using phenolphthalein as the only indication? My guess is both hydrogens from the oxalic would be strong enough ionized in solution for that one indicator to be good enough; but my judgement could be wrong (unless I review the theory thoroughly).
 
  • #11
oxalic_acid_titrated_with_sodium_hydroxide.png
 
  • #12
Borek has given a graphical clarification about the endpoint pH's for the titration so that surely helps. If you want to go to both endpoints, then this will be titrating for BOTH hydrogen ions from the oxalic acid. Notice that the more endpoint to pH 2.8 is not going to be very sharp; maybe this means you would want to take just the first enpoint, for which phenolphthalein would be the suitable endpoint (for ONE hydrogen ion).
 
  • #13
On the second thought the problem is this question is poorly defined. It doesn't specify what it means by "needed to neutralize". If taken literally (and that would be my approach), oxalic acid is diprotic. If it is about titration, only the first end point is sharp enough to be usable. That gives two possible answers that differ by exactly 100%.

sodium_hydroxide_titrated_with_oxalic_acid.png
 
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1. What is ionic equilibrium titration?

Ionic equilibrium titration is a chemical process of determining the concentration of an unknown solution by reacting it with a known solution of an acid or base. This titration is based on the principle of ionic equilibrium, where the concentration of ions in a solution is dependent on the equilibrium between the dissociated and undissociated forms of an acid or base.

2. How is ionic equilibrium titration different from other types of titration?

Unlike other types of titration which rely on the neutralization of an acid and a base, ionic equilibrium titration involves the measurement of the concentration of ions in a solution. This type of titration is also used for weak acids and bases, as it takes into account their dissociation constants and equilibrium equations.

3. What are the key components involved in an ionic equilibrium titration?

The key components in an ionic equilibrium titration include a burette for dispensing the known solution, an indicator to signal the endpoint of the reaction, and a pH meter to measure the pH of the solution. The unknown solution and the known solution of an acid or base are also essential components.

4. How is the endpoint of an ionic equilibrium titration determined?

The endpoint of an ionic equilibrium titration is determined by the use of an indicator. The indicator is a substance that changes color at a specific pH range, which corresponds to the endpoint of the titration. The color change indicates that the reaction has reached equilibrium, and the endpoint is achieved.

5. What are some common applications of ionic equilibrium titration?

Ionic equilibrium titration is commonly used in the pharmaceutical industry to determine the concentration of drugs in a solution. It is also used in environmental testing to measure the concentration of pollutants in water. Additionally, this type of titration is used in research and development to study the dissociation constants of different acids and bases.

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