Back titration of Vanadium with Iodine Starch complex. Watch

Baq99
Badges: 0
Rep:
?
#1
Report Thread starter 4 years ago
#1
Hey folks, I'm totally stuck on a lab report for uni. Have to get it done for after new year and I've just hit a mental block. I reduced a standard solution 2.2 vanadium solution (25ml) diluted to 50ml. Added 50ml 1M sulphuric acid and 1 g of potassium iodide. I then titrated the liberated Iodine with 0.1 M sodium thiosulphate using starch as an indicator. My titre was 13.1cm^3.

How do I work out the oxidation state of vanadium before titration?

Any help would be amazing! Fankooo!
0
reply
hannahc072
Badges: 7
Rep:
?
#2
Report 4 years ago
#2
Don't know if this helps but vanadium has 4 common oxidation states which can be distinguished by its colour:
yellow = +5
blue = +4
green = +3
violet = +2
0
reply
username986184
Badges: 3
Rep:
?
#3
Report 4 years ago
#3
(Original post by Baq99)
Hey folks, I'm totally stuck on a lab report for uni. Have to get it done for after new year and I've just hit a mental block. I reduced a standard solution 2.2 vanadium solution (25ml) diluted to 50ml. Added 50ml 1M sulphuric acid and 1 g of potassium iodide. I then titrated the liberated Iodine with 0.1 M sodium thiosulphate using starch as an indicator. My titre was 13.1cm^3.

How do I work out the oxidation state of vanadium before titration?

Any help would be amazing! Fankooo!
Not enough info in your question.

What does "standard solution 2.2 vanadium solution" mean?
0
reply
Baq99
Badges: 0
Rep:
?
#4
Report Thread starter 4 years ago
#4
Hi folks,

I think I have it. As the end point was blue that means the oxidation state was 4+.
I work out the moles of the 0.1 M sodium thiosulphate and the moles of vanadium. I then use the half equation of sodium thiosulphate:
2S2O3(2-) ---> S4O6(2-) + 2e-
to figure out I have 2 moles of electrons for every one mole of S4O6(2-). I then multiply the moles of sodium thiosulphate by 2 to work out the moles of electrons transferred and ratio the moles of electrons against the moles of vanadium. This results in 1:2 ratio meaning I take 2 from the end point 4 to figure out vanadium was in the 2+ state before titration...

I think. I thought I'd post my solution just in case anyone does anything similar in the future.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Sheffield Hallam University
    Get into Teaching in South Yorkshire Undergraduate
    Wed, 26 Feb '20
  • The University of Law
    Solicitor Series: Assessing Trainee Skills – LPC, GDL and MA Law - London Moorgate campus Postgraduate
    Wed, 26 Feb '20
  • University of East Anglia
    PGCE Open day Postgraduate
    Sat, 29 Feb '20

Do you get study leave?

Yes- I like it (150)
60.73%
Yes- I don't like it (11)
4.45%
No- I want it (69)
27.94%
No- I don't want it (17)
6.88%

Watched Threads

View All