[mahi123]

Hey, we did a titration lab, I need help with 3 questions, I looked in the book, online but can't seem to find an answer, so here it goes,  we used KHC8h4o as the acid in the standarization titration, and it asks why we used it.
Also it asks why we should not shake KHC8H4O before titrating it, and lastly why is boiled distilled water used to prepare solutions?? I've searched but couldn't find any answers so if someone can helppppp!!!!!

[Dan]

Now first it says dissolve 10 grams in 50 ml water, so concentaration becomes 0.005 moles/ml, or 5 moles/L. Then it says dilute it with 500 mL, so I'm confused as to how to calculate the final concentration from here. I have initial concentration, then 500 mL, so how do I get the final concentration?

And also why is boiled distilled water used to prepare solutions?? But I mostly need help with first quesion so thanks,

The thing here is that it depends on whether your 50 mL of 5 mol/L solution was diluted with 500 mL water or diluted to 500 mL.

In either case, just work it out by using your 0.25 mol in 550 mL or 500 mL for the with and to cases respectively. I suspect it's the latter case as this gives you a nicer number, but check your procedure again.

[mahi123]

Hey thanks for the help, I actually did that question so I erased it from my post. By the way, it's dilute with 500, so total adds to 550. Now I need help with those 3 questions lol.


Edit: Okay, I also got the answer to first one, we use it because it's a common primary standard( whatever that means), so it's pure and its stated conecentrations are accurate... Now I need answers to last two questions, why do we not shake it ,and why do we use boiled, distilled water!!!

[Borek]

What gases are present in the air?

[mahi123]

oxygen, nitrogen


it's related to which question? where we don't shake phk or with the boiled, distilled water?


Also for boiled distilled water, is it because it's pure, it doesnt contain ions like chlorine because if it did, it would affect the results of the labs and we would get inaccurate result, is that a good answer

[Borek]

oxygen, nitrogen

That's not all. Try harder

[mahi123]

carbon dioxide?
 argon?

[Borek]

carbon dioxide?

Assuming it is CO₂ - why do you use boiled water, why don't shake, what effect dissolved CO₂ may have on the reagents used and the final result?

[mahi123]

i don't know, that's why i made this thread

[Borek]

I think you know, you just can't connect loose ends. Your titration is an acid/base titration, you will be using some strong base (like NaOH) as titrant. How does CO₂ react with strong bases?

[mahi123]

I think you know, you just can't connect loose ends. Your titration is an acid/base titration, you will be using some strong base (like NaOH) as titrant. How does CO₂ react with strong bases?

Thing is I have to hand this in soon. And I don't know much about titration, we didn't complete this section, we are only doing the lab, and we only got instructions for it and even for that I missed a class. But Anyway, I found this equation and information online:
CO2 (g) + NaOH (aq) ------> H2CO3 (aq) + NaHCO3 (aq)
Because the resulting mixture includes both a weak acid and a weak base, adding either strong acid or strong base (NaOH, or sodium hydroxide) does not change the pH very much.
If a strong base, such as sodium hydroxide, is added, the pH does not become very much higher because some of the H2CO3 is converted to NaHCO3. The NaHCO3 does not give a very high pH because NaHCO3 is a weak base. Thus the pH can neither become very low nor very high. The mixture of H2CO3 and NaHCO3 acts as a buffer. A buffer resists a change in pH.

Is this what you're getting at?

[Borek]

Is this what you're getting at?

Nope. Thing is much simpler - if there is CO₂ dissolved in the solution you are titrating two acids, not one (KHP).

Equation you have listed doesn't make sense. NaOH plus CO₂ gives either sodium bicarbonate or sodium carbonate, not mixture of bicarbonate and carbonic acid.