Tricks of the trade

[stonecold]

So does that rule apply if you add more water to the conical flask where the 'unknown' is placed?

Ok. There you go. An exception. If you add water to conditions that are not the norm......
is that better?




Pedantic.

Uh, wouldn't that just have no effect, as the mol hasn't changed?

[Stroodle]

That  just made me dizzy  :uglystupid2:

[naved_s9994]

Guys, there HASSSS to be something out there, thats make it crystal clear!
Its really pissing me off now.

Lets do a World wide world search for tricks on this, for Gods sake!

[azn_dj]

So does that rule apply if you add more water to the conical flask where the 'unknown' is placed?

Ok. There you go. An exception. If you add water to conditions that are not the norm......
is that better?




Pedantic.

Uh, wouldn't that just have no effect, as the mol hasn't changed?

I know. But someone decided to be pedantic!
Anyways, the way I look at it is if you add more mol, you have to take out water.
so more mol in known = less water in known.

[stonecold]

Yeah, I'm just trying to combine those rules with yours so we can have a neat little six line formula that covers everything haha...

[naved_s9994]

Yeah, I'm just trying to combine those rules with yours so we can have a neat little six line formula that covers everything haha...

Appreciated !

[stonecold]

okay, i'll sit down and see if it works.

[Stroodle]

I just always bring it back to the titre being larger or smaller, cause that's what u directly use in your calculations to work out the amount of your unknown.

[Martoman]

Guys come on.

If you have less. You need to add more. Pretty simple?   

[stonecold]

Golden Rules for titration errors
1. If you rinse the unknown glassware with water, your calculated concentration is lower.
2. If you rinse the known glassware with water, your calculated concentration is higher.

Sub rules
Adding more mol to the known is equivalent to rinsing the unknown glassware with water (Rule 1 applies)
Adding more mol to the unknown is equivalent rinsing the known glassware with water (Rule 2 applies)
Rinsing unknown with known is equivalent to rinsing the unknown glassware with water (Rule 1 applies)
Rinsing known with unknown is equivalent to rinsing the known glassware with water (Rule 2 applies)

Note:  Rinsing the conical flask with water will have no effect on the result.

I think this is right, please check and/try it out to confirm.

[azn_dj]

Yeah thats all right. Im not a big fan of the logic though. I would prefer subtracting water, because it feels like its crossing from one to the other a bit too much.
But yeah, it works out nicely, until you try to explain it. Hahaha.

Note: 50th post! Can now give karma!!

[stonecold]

I can explain it

If you add known to known, then you need more unknown for the titration.  The same as if you dilute the unknown, you need more for the titration.

If you add unknown to known, then you have done a mini reaction, and mol of known has been reduced, hence a smaller titre is needed.  The same as if you just dilute the known.

And by dilute, I actually mean you are displacing a small amount of solution with water, hence some mol is lost.

TBH though, I just prefer to do the math.  I find it easier to work out on the spot.

[naved_s9994]

Golden Rules for titration errors
1. If you rinse the unknown glassware with water, your calculated concentration is lower.
2. If you rinse the known glassware with water, your calculated concentration is higher.

Sub rules
Adding more mol to the known is equivalent to rinsing the unknown glassware with water (Rule 1 applies)
Adding more mol to the unknown is equivalent rinsing the known glassware with water (Rule 2 applies)
Rinsing unknown with known is equivalent to rinsing the unknown glassware with water (Rule 1 applies)
Rinsing known with unknown is equivalent to rinsing the known glassware with water (Rule 2 applies)

Note:  Rinsing the conical flask with water will have no effect on the result.

I think this is right, please check and/try it out to confirm.

Q1.Known is thing in burette, Unknown in conical flask?
Q2.Adding more mol of what to known/unknown , (first two points?)

[Martoman]

uhhhhhhhhhhhh i don't like rules. I like intuition.


So if i have something in burette. And i wash it with water.

This means that there is less mol in the burette. Which means less mol wil react in the conical flask. Which means concentration in the flask is lower yes?

[naved_s9994]

uhhhhhhhhhhhh i don't like rules. I like intuition.


So if i have something in burette. And i wash it with water.

This means that there is less mol in the burette. Which means less mol wil react in the conical flask. Which means concentration in the flask is lower yes?

c=n/v

Yes, your right.