EDTA question. (1 Viewer)

[Sparcod]

So why was the concentration of Ca higher than it shoul be?

 

[Harry Seacombe]

I said there may have been a mistake in the titration, one value higher than the three others. This would have increased the average concentration and made the calcium concentration seem higher.

 

[CheekyPunk]

I said the same, though i think its something different. Titrations are pretty accurate, cause you do them a few times over.

 

[bumble bee]

I said that the titration would have caused it because you always put a few drops over for the indicator to actually change colour.

 

[Harry Seacombe]

I said the same, though i think its something different. Titrations are pretty accurate, cause you do them a few times over.

Normally the first one is a bit higher because you overshoot the equivalence point.

 

[bboyelement]

i talked about the buffer lol, it uses up or something lo.

hahha yeh thats what i said too because it couldnt be an error since they did it several times
and it was obvious as well cause if i remember correctly we dont add buffer in titration...

 

[angmor]

i just said that AAS is alot more accurate than human experimenting.

 

[OToole]

Other dissolved ions in the water.

 

[[Damo]]

the standad solution of EDTA may have been dissolved in water that was not de-ionised. So there may have been calcium ions already present as in hard water, hence the greater concentration of Ca ions using the volumetric method.

 

[followme]

Normally the first one is a bit higher because you overshoot the equivalence point.

yep, the rough titre shouldnt be used in calculation, as it is only performed to find the approx. position of the end point.

 

[earthnfire]

I said AAS is more accurate and i added that the person may have included a titre value that was way of in the average...except in more scientific words...Lol

 

[sja]

It said IDENTIFY A REASON

Hence I just wrote...

"Incorrect method of titration."

WOO!!

 

[dunno04]

The solution is too concentrated
therefore it is not that accurate

 

[rtsk]

Other dissolved ions in the water.

Most certainly... and that's by far the most significant one.

 

[toadstooltown]

Yes, EDTA measures hardness of water -- *both* Ca2+ and Mg2+ ions are chelated by it in the titration with erichrome black T (indicator). So clearly the 16% extra was actually Mg2+.

 

[sam15_]

pretty much.. we umm NEVER did titration because our teacher said it was boring.. hence of course the 100 million marks on titration in the test... so srewed... i think i wrote about maths... theoretical and experimental probablitiy... good try right

 

[ringout13]

i just said that AAS is alot more accurate than human experimenting.

haha me too

 

[aaaazzzz]

the answer is they include the trial result
it said the titration was repeated three times
so they did 4 times
but they use the average of all 4

 

[[Damo]]

i think that saying they averaged wrong, i.e; included the rough volume, is not sufficient, its too much of an assumption thats not well justified, otherwise the markers will have to accept all titration errors for the qt answer, i.e, didn't rinse properly, etc...
so i think the answer is the fact that there were other ions present or even possibly extra Ca ions in the standard

 

[Nodice]

Definately the Mg2+ ions accounting for that 16%. It said that it reacts with magnesium and calcium for a reason.