errors for titrations (1 Viewer)

[hobbit]

HI, can somebody plz tell me the all possible errors in titrations. I'm not sure which are valid and which aren't. For example I know that reading the miniscus wrong is not a valid error. Plz Help!

 

[hipsta_jess]

washing the materials out with the wrong stuff...like washing the burette out with water would give a false reading...

 

[Collin]

You must wash out the equipment you're using with the substance you're putting in. An exception is the substance you're titrating for in the beaker, in which the important thing is the number of moles of that substance. For example, after if you want to transfer say 25mL of NaOH to the beaker for titration, it would not matter if you wash it with distilled water before hand, because the important thing is that there is 25mL equivalent moles of NaOH in that beaker. However for the burette you MUST wash it with the substance that's going in, or else it would modify the mole ratio of that substance vs whatever you washed it with in the burette.

A good idea is to put labels on all your beakers/flasks etc. so there is no mix up. Another good idea is to use a control, that is if you are looking for a colour change of a certain colour due to adification for example, it would be wise to set up such an acid with a bit of indicator in the first place before the titration so that you can easily match it up with your titration to spot the end point.

Another error is once you're around your end point, swirl the beaker for a good few moments before adding another drop. Sometimes the substance takes a few seconds before even starting to change to another colour.

 

[tina_goes_doo]

To determine the actual end-point in the titration is subjective and where the titration changes colour varies for each person.

It's not really an error but a good idea is to note that once the titration is over, you are actually a small quantity over the amount needed for neutralisation. Therefore there would be a slight error in the calculations, which is unavoidable.

 

[CM_Tutor]

Originally posted by tina_goes_doo
It's not really an error but a good idea is to note that once the titration is over, you are actually a small quantity over the amount needed for neutralisation. Therefore there would be a slight error in the calculations, which is unavoidable.

Actually, you are a small amount beyond the equivalence point, which is what you are trying to find. This is not the same thing as neutralisation.

 

[tina_goes_doo]

Dang, no wonder i suck at chemistry...

 

[xiao1985]

tell me abt it...
i HATE HATE HATE HATE titration!!!!!! n we got to be assessed on it this thurs!!!!!!!! i heard if we got out of 1% range, we got 0 !!! @@

aniwaz, the practice run i did horribly... around2-3 % off usually =( major bummer, i am gonna fail chem =(

things like rinsing your glass ware, pure primary standard, readings, everything affects your readin =(

 

[CM_Tutor]

Originally posted by xiao1985
n we got to be assessed on it this thurs!!!!!!!! i heard if we got out of 1% range, we got 0 !!! @@

You heard wrong.

 

[tina_goes_doo]

Oh god we just got the marks back for our titration assessment. The damn teacher marked so hard! The highest mark in our year was 18.5 / 20 (at a selective high school!)

Things he marked us down for:

1/ if our results were not in table format. Forget a nice little column for the results, neatly set out et al, he wanted headings. GRRR....the instructions never told us it was meant to be in a table.

2/ He wanted the correct number of significant figures IN THE CALCULATIONS! That meant multiplying stuff by 0.0250 which really makes no difference if you leave out the 0 at the end. It's only the bloody calculations!

And now i can't remember what else was wrong with it...

Last assessment task he told us that in the whole year, there was probably only one person who would possibly manage a band 6 in the HSC. The rest of us suck!

 

[t-i-m-m-y]

if u tend to be generous, and appreciate the broad spectrum of light. u dispense lots of the reactant from the burette(generosity), and i like deep pink colours lol. now that makes good end point lol

significant figures indicate ur expected degree of accuracy, its bloody important at uni

 

[Kirsti]

actually, they told us before the test that they wanted 4 DECIMAL PLACES then marked us down for not having 4 sig figs!
lol, then where they corrected it they used 5 sig figs.

We got marked down for not having a bloody border around our table of results. What the?

 

[iambored]

Originally posted by Kirsti
actually, they told us before the test that they wanted 4 DECIMAL PLACES then marked us down for not having 4 sig figs!
lol, then where they corrected it they used 5 sig figs.

We got marked down for not having a bloody border around our table of results. What the?

yeah once i got marked down for a similarly stupid thing

mistakes -

don't contaminate each of the liquids that you have with each other!

remember that when you are pouring into the burette, sometimes some runs down the side to the bottom, so it should be wiped before you start the actual titration

also remember to get the bubbles out of the bottom of the burette (flick it and let some run out)

 

[tina_goes_doo]

Originally posted by Kirsti
actually, they told us before the test that they wanted 4 DECIMAL PLACES then marked us down for not having 4 sig figs!
lol, then where they corrected it they used 5 sig figs.

Yeah well at least they're remarking your tests! Notice how it's only your class btw...

 

[tina_goes_doo]

Btw, for all the people who said possible errors could occur with the washing/rinsing of the equipment, our teacher said that was not a valid error. I know coz he friggin gave me zero for that! If anyone wants to disagree, I'll be happy to hear it.

Ok so what about if you have a question following that - what improvements could you do/have done in the titration?

These are all i could think of:

1/ used a white tile or white paper (for the whole subjective colours thing)

2/ perform a number of titrations to decrease the margin of error.