Help needed with Chemistry AS practical!

[flyingcrayons]

Hi all,

In the titration involving the starch indicator, the question asks to run the solution into the conical flask "until the initial red/brown colour of the iodine becomes pale yellow". Do we stop running the solution when it just turns yellow or REALLY pale yellow? How do we judge the colour?

Also, I would like to know how a proper limewater test and potassium dichromate test are done.

Any help is very much appreciated. Thanks!

 

[rosh2o_q2o]

you can put a little drop of k2cr2o7 into the filter paper then put some drops of solution to be tested on the k2cr2o7 of the filter paper.then it will turn to green from orange. This how i do this. there might be some other way this....i think best of luck

 

[mohib]

ANY GUESSES?????? BOUT PRACS p34?

 

[eva 21]

you can put a little drop of k2cr2o7 into the filter paper then put some drops of solution to be tested on the k2cr2o7 of the filter paper.then it will turn to green from orange. This how i do this. there might be some other way this....i think best of luck

WOW!!!
thanks! that was neat.

 

[maars12345]

Any idea or clue abt da question paper of P34

 

[MAVtKnmJ]

You can also take a little bit of the solution in a test tube and then add K2Cr2O7 into it to see if it changes from orange to green

Regarding the titration question, it usually states in the question that "Don't add too much of FB3 at this point" so I'd say add a little bit of FB3 about 3-5 cm^3.
In these kind of questions, it's hard to figure out the color changes / end points that's why the examiners are usually lenient in marking, so don't worry! A marker in these questions is that usually the end point will be reached above 15 cm^3 and below 20 cm^3

Hope that helps!