Sodium Acetate pH - 0.2M Solution, No Acetic Acid Added

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In summary: If not, you can calculate it using this equation:slope = (conc. - baseline) / conc.If you can't find a slope, then the electrode may be old or the solution may have been changed recently.
  • #1
philip041
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I have 0.2M solution of Sodium Acetate, (100ml with 1.6g NaAc)

I want to work out the pH it should be. THERE IS NO ACETIC ACID ADDED.

This is causing me nightmares! I am measuring ph 6.5 but apparently that is wrong. Why would that be so?

Cheers!
 
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  • #2
Do you know what pH should it have?

How are you measuring pH?
 
  • #3
Well I was told by someone in my lab they remember it should be pH8. I found some botch eqn but worked out that maybe it should be pH9?

I am using some super fancy pH meter, the glass tube ones. I double checked against another one and it turns out its not so fancy after all. I measured pH7 with a different one, however this is still low. Especially shouldn't the pH go UP when you NaAc?

I think the eqn was, (sorry no Latex):

pH =0.5 * (14 +pKa + log(Ci)) where Ci corresponded to the molar something, o.2

Cheers
 
  • #5
yeah I worked out 9.03 or something. pH meter was recently calibrated yet seems to still give 0.5 pH below another pH meter in dept. I think it highly unlikely that that one is also wrong as it is used constantly by a research group and they would have to be pretty careful about things like that.

We were careful with our measurements, we wash everything, we use really pure water, what is going on!
 
  • #6
Calibrate your electrode and leave the probe in the sodium acetate solution for about 10 minutes. Prepare a fresh solution of sodium acetate and measure that solution.

What solution do you store the electrode in? What is the slope of your electrode?
 
  • #7
I don;t know what we store it though I will find out tomorrow. it is stored vertically.
 
  • #8
philip041 said:
pH meter was recently calibrated

What do you mean by "recently"? Calibrate it now to be sure.
 
  • #9
Will calibrate now, it is in saturated KCl, as normal I think for these things
 
  • #10
philip041 said:
I don;t know what we store it though I will find out tomorrow. it is stored vertically.
:biggrin: Very funny! Of course I was referring to the http://biology.bard.edu/ferguson/course/bio141/Lab/Lab_Appendix_1.pdf" procedure...

Saturated KCl is not a standard storage solution (its what is used in the filling solution in many electrodes, though). It will likely salt up the bridge. It is more common to store the electrode in a pH 4 or pH 7 buffer solution.
 
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  • #11
Hmm I will ask my supervisor again, as I also thought it odd thwe ownat it would be stored in that. I think maybe we have solved the problem, the set of standards , (fluka analytical ph 4,7,10) were chosen from a list and ours was probably set to the wrong one so we changed it to the set which seemed most appropriate(fisher).

however still doens;t explain why we measure pH 7.5 for something which should be 9.

We used 1.6g of NaAc for 100 ml water, to make o.2M soln?
 
  • #12
I think maybe the elctorde is wrong actually, when we make a measeurement it takes absolutly for ever to stabablise. It will keep climbing really slowly until it reaches a plateau but this can take 10-15 minutes, why the delay?
 
  • #14
Does sound like a cooky electrode.

What kind of sodium acetate are you using? Is it anhydrous or hydrated? That could effect your expected concentration by almost half. Check the reagent bottle as well or you could try a quick and dirty titration to see if that changes anything.
 
  • #15
Won't hurt to check the concentration, but to get below pH 8.0 you need to dilute sodium acetate to 2e-3M, this doesn't sound likely.
 

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  • #16
philip041 said:
I think maybe the elctorde is wrong actually, when we make a measeurement it takes absolutly for ever to stabablise. It will keep climbing really slowly until it reaches a plateau but this can take 10-15 minutes, why the delay?

Did you record the slope for the electrode during your calibration procedure?
 

Related to Sodium Acetate pH - 0.2M Solution, No Acetic Acid Added

1. What is the purpose of a 0.2M solution of Sodium Acetate with no added Acetic Acid?

A 0.2M solution of Sodium Acetate with no added Acetic Acid is used as a buffer solution to maintain a stable pH level in a variety of experiments and processes. It can also be used as a reagent in chemical reactions.

2. What is the pH of a 0.2M Sodium Acetate solution with no added Acetic Acid?

The pH of a 0.2M Sodium Acetate solution with no added Acetic Acid is typically around 8, making it slightly basic. However, the exact pH may vary depending on the concentration and purity of the solution.

3. Can Sodium Acetate be used as a substitute for Acetic Acid in experiments?

No, Sodium Acetate cannot be used as a substitute for Acetic Acid in experiments that specifically require Acetic Acid. However, it can be used as a buffer solution in some cases where Acetic Acid is not necessary.

4. How is the concentration of a Sodium Acetate solution determined?

The concentration of a Sodium Acetate solution can be determined by measuring its molarity, which is calculated by dividing the moles of Sodium Acetate present by the volume of the solution in liters.

5. Is it safe to handle a 0.2M solution of Sodium Acetate with no added Acetic Acid?

Yes, a 0.2M solution of Sodium Acetate with no added Acetic Acid is generally safe to handle. However, as with any chemical substance, it is important to follow proper safety precautions and handle it with care to avoid any potential hazards.

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