[ezmenightin]

Hi,

for my individual A level chemistry investigation i am looking at the calcium content of milk. We have to use two different methods. I have been told that i could titrate the milk with two different substances. I know that i can use EDTA, however i am kind of stuck with what else i could use.  Having done some research i have found that i could use NTA however i have also found that this is known to be a carcinogen,so it is highly unlikey that i will be allowed to use this.  Does anybody have any suggestions as to what else i could use to determine the calcium content of milk?

[Borek]

Does the second method have to be titrimetric? I remember some gravimetric methods but no other titration.... black hole in brain

[ezmenightin]

Im not entirely sure what gravimetric methods are?When I asked my teacher what I should do for my second method, she said that i could do another titration with another chelating agent which complexes with calcium?Im just not entirely sure what other chelating agents complex with calcium other than EDTA.

[Borek]

Im not entirely sure what gravimetric methods are?

Precipitate, filter and weight. In case of calcium you precipitate oxalate and weight it after drying as oxalate, or - after roasting - as CaO.

When I asked my teacher what I should do for my second method, she said that i could do another titration with another chelating agent which complexes with calcium?Im just not entirely sure what other chelating agents complex with calcium other than EDTA.

Most of them. For details you have to look into textbooks (or start checking which reagents are in the lab, that should give you an idea which method can be used). My textbooks are in Polish, so they will be of no help to you

What I don't like in this approach is that basically you are doing second almost identical determination, as all complexometric titrations are similar, regardless of chelating agent used.

[sdekivit]

Im not entirely sure what gravimetric methods are?When I asked my teacher what I should do for my second method, she said that i could do another titration with another chelating agent which complexes with calcium?Im just not entirely sure what other chelating agents complex with calcium other than EDTA.

the chemicals they use to keep blood from clotting are:

Na-EDTA, Na-citrate and Na-oxalate (3 chelating agents). With the last 2 chemicals you can do a gravimetric titration because Ca-citrate and Ca-oxalate are insoluble.

[Borek]

you can do a gravimetric titration

What is a gravimetric titration?

[sdekivit]

a precipitation titration where you do a gravimetric analysis on.

[Borek]

a precipitation titration where you do a gravimetric analysis on.

I don't get it, please elaborate. Precipitation titration an gravimetric analysis are completely different analysis methods.

[sdekivit]

i know these are two different things. Gravimetric titration is not a commonly used term. But is just a titration were the precipitate gained by the titration is analysed by gravimetry.

read for example http://www.freepatentsonline.com/5006312.html

the precipitation titrations are for example argentometry. And,true, gravimetry is not a common titration analysis, but sometimes you have a sample that you don't know the content of. With gravimetry you can add till 10% excess of reagent. Not more. So it's done by titration.

[Borek]

Gravimetric titration is not a commonly used term. But is just a titration were the precipitate gained by the titration is analysed by gravimetry.

read for example http://www.freepatentsonline.com/5006312.html

Perhaps my Enhlish fails me, but from what I read at the link provided precipitate has nothing to do with the method - "gravimetric" in this case means just that balance is used to measure amount of titrant added. So it seems to me that "gravimetric titration" is just a titration with balance used instead of burette scale.

[Mitch]

Perhaps my Enhlish fails me, but from what I read at the link provided precipitate has nothing to do with the method - "gravimetric" in this case means just that balance is used to measure amount of titrant added. So it seems to me that "gravimetric titration" is just a titration with balance used instead of burette scale.

Sounds right to me. Aside from Enhlish

[Borek]

Sounds right to me. Aside from Enhlish

Oops, it failed  

[ezmenightin]

the chemicals they use to keep blood from clotting are:

Na-EDTA, Na-citrate and Na-oxalate (3 chelating agents). With the last 2 chemicals you can do a gravimetric titration because Ca-citrate and Ca-oxalate are insoluble.

So...if i used Na-Oxalate to titrate the milk with...i would get a precipitation of Ca-oxalate....how would i then tell how much calcium there is? I am soooo confused!

[kevins]

Im not entirely sure what gravimetric methods are?When I asked my teacher what I should do for my second method, she said that i could do another titration with another chelating agent which complexes with calcium?Im just not entirely sure what other chelating agents complex with calcium other than EDTA.

The other chelating agent for Calcium:
1. EGTA
2. CDTA
Please try.

[sdekivit]

So...if i used Na-Oxalate to titrate the milk with...i would get a precipitation of Ca-oxalate....how would i then tell how much calcium there is? I am soooo confused!

the Ca-oxalate can be weighed and than you can calculate the amount of mols Ca.