[dantex3]

1. Vitamin C is an acid (ascorbic acid) and a reducing agent . which property is utilized for its analysis?

2.  a) What is the oxidizing agent in Experimental Procedure , Vitamin C Analysis?
 
     b) What is the colour change of the starch indicator that signaks the stoichiometric point?
   
     c) What is the purpose of adding sodium bicarbonate to the ascorbic acid sample ? write a balanced equation for its reaction
   
     d) The NaHCO3 sollution is omitted in an analysis of a sample . Will the reported amout of ascorbic acid in the sample be too
        high , too low , or unaffected ? Explain.

3 . a) After adding the standard solution of KIO3 , the KI , H2SO4 and NaHCO3 sollutions , the sample solution remains colourless!
        What modification of the experimental procedure can be made to correct for thos unexpected observation in order to
        complete the analysis?
   
     b)The deep-blue colour of the I2 . starch complex does not appear !What next? Should you continue titrating with the
         standard Na2S2O3 solution or discard the simple ?Explain

Plz help me!!! thz for everyone..     

[cliverlong]

The text of your question uses the words "Indicator" and "titrating" so I entered the phrase

titrating ascorbic acid

in Google

the first two entries I got in my list were

http://chemistry.about.com/od/demonstrationsexperiments/ss/vitctitration.htm
http://en.wikipedia.org/wiki/Ascorbic_acid

Scanning through them they both refer to using

iodine/starch
or
iodine/iodate

as indicators.

These seem to fit quite a lot of keywords  in your question. I suggest you study these articles and maybe search for some more, then see if you can apply the ideas to your question. Please post back your attempts and your working.

Clive

[dantex3]

The text of your question uses the words "Indicator" and "titrating" so I entered the phrase

titrating ascorbic acid

in Google

the first two entries I got in my list were

http://chemistry.about.com/od/demonstrationsexperiments/ss/vitctitration.htm
http://en.wikipedia.org/wiki/Ascorbic_acid

Scanning through them they both refer to using

iodine/starch
or
iodine/iodate

as indicators.

These seem to fit quite a lot of keywords  in your question. I suggest you study these articles and maybe search for some more, then see if you can apply the ideas to your question. Please post back your attempts and your working.

Clive

i think i upload my notes will much better