chemistry question

[perrychan527]

State what u would see as iron(II) ions in solution are titrated with potassium manganate(VII). How would u detect the endpoint of the titration?(3)

Ans: purple colour of MnO4- lost (1)
endpoint when yellow/ colourless solution (1)
becomes permanently pink (1)

I dont know what does it mean. I know purple is lost as MnO4- is reduced to Mn2+. The yellow is due to Fe3+, but why permanently pink?
Thank guys  

[cashem'up]

this is because when the color is permanently pink it shows that all the Fe has reacted and the MnO4 reduced and that the extra drop of KMNo4 goes to show that the reaction is complete as this drop is not reduced due to the lack of color change.
hope it helps
 

[nid404]

Paper?

any particular indicator mentioned?

[perrychan527]

i got some of ur pt. What did u mean is that the extra drop of MnO4- is purple itself, but when it goes to a large amount of colourless solution, solution become pink?

[perrychan527]

no indicator

[cashem'up]

i got some of ur pt. What did u mean is that the extra drop of MnO4- is purple itself, but when it goes to a large amount of colourless solution, solution become pink?

yea see if it becomes purple then it goes way off the end point as there is too much excess however when only one drop excess added there will be a faint permanent pink color that wont go even if u shake it, yes as u said a purple drop in large colorless soln will be pink.......

[XaM!!]

yea see if it becomes purple then it goes way off the end point as there is too much excess however when only one drop excess added there will be a faint permanent pink color that wont go even if u shake it, yes as u said a purple drop in large colorless soln will be pink.......

ya agreed... when ur titrating at some point sol becomes v.light yellow, that is v.near to end point... it means that a single drop could be in excess... like half of a drop is needed to complete reaction so a full drop makes the colour pure pinkish which is not required vvlight pink is the endpoint...


 n nid indicator isnt used in back titration...

[cashem'up]

Paper?

any particular indicator mentioned?

yea actualy pretty much wen kmno4 is being reduced in a reaction the color change itself is the indicator so u dont really need an indicator