CHEMISTRY. P3. CIE.. advice and titrations?

[master786]

tomororw

[LLawliet81]

I think it will be identification, thermochemistry and find molarity.

Anyone knows about identification of Cobalt ? Need help

[poisonedrose]

I have a feeling there will be identification of ions, enthalpy change and water of crystallization.

[LLawliet81]

What is the example of crystallization experiment ?

[winnie101]

anyone who has done mj 09 paper 31, could u plz explain the mole questions in part c. i just get how to do the first 2 moles questions
Thanks

[Phosu]

i) for first step they have given u the concentration, ur titre value is the vol of Na₂S₂O₃
so to find moles apply n=cv, n= .15 x titre/1000

ii) next is simple mole ratio which can be found from the equations
S₂O₃^2- : I₂
  2 : 1
  i) : x

iii) again its the same as above
Cu²⁺ : I₂
  2 : 1
  x : ii)

iv) now we know the moles present in Cu²⁺ and we have the volume (25cm³ dissolved in FA3)

  iii) = c x 25/1000

v) im not really sure bout this one

[ruby92]

M/j 2009 variant 32
c step 3 4 5???

[aldehyde1612]

im not sure but i think the last step involves C₁*V₁ = C₂*V₂

so.. concentration of FA2 = concentration of FA3*Volume (250 or something) divided by Volume of FA2 buretted (the amount at the beginning when making FA3)

if that makes sense.  

[superduper2009]

how do find water of crystallization???

[XaM!!]

For water of crystallisation just follow the instructions... basicaly a test tube and a salt is given. a specific mass is asked. first u have to find mas of empty test tube. thn add salt and measure mass(mass is gven in ques whch u have to take).
now heat the test tube at medium flame. do it for 5-8 mins to ensure water is eliminatd. nw cool the tube n measure mas. again heat the test tube for another 5mins n cool n measure, thn compare if masses r the same as the recent one thn all the water is eliminated... if the mas is change thn again heat n measure mass. when it becomes constant. nw use this mass for further calculations to calculate X in salt.X.H2O... that x is water of crystallisation...

[joggingday]

M/j 2009 variant 32
c step 3 4 5???

Step 3:
To calculate moles of ethanedioate ions that reacted with the KMnO4 : Use the mol ratio from 2nd step. You find that for every 2 mol of MnO4- ions, there are 5 moles of ethanedioate ions. So :
 
Answer = (Mol of KMnO4/2) * 5

Step 4: You know the volume of FB3 used in the titration was 25 cm3. So molarity = mol of ethanedioate ions/volume in dm3
Volume in dm3 will be 25/1000= 0.025

Step 5: You now have the concentration in mol dm-3 from step 4. This tells you that there are x mol in 1000cm3. You have to multiply this value by 1000 to get the "total" moles. Then divide this answer by the volume of FB2 used (which should be between 42.5 and 43.0 cm3)

Step 6: From step 5 you have the number of moles per dm3. To find the amount of grams per dm3, simply multiply your answer in step 5 by the Mr, to get the mass per dm3. In this case it will be:
concentration * 126

Hope this helps

[Ro1024]

hey, could anyone who does the exam earlier post some of the questions that come up?
cos i am reallly crap at practicals! let me know, i do it on thursday! PAPER 31...
Anyone??

[ruby92]

Step 3:
To calculate moles of ethanedioate ions that reacted with the KMnO4 : Use the mol ratio from 2nd step. You find that for every 2 mol of MnO4- ions, there are 5 moles of ethanedioate ions. So :
 
Answer = (Mol of KMnO4/2) * 5

Step 4: You know the volume of FB3 used in the titration was 25 cm3. So molarity = mol of ethanedioate ions/volume in dm3
Volume in dm3 will be 25/1000= 0.025

Step 5: You now have the concentration in mol dm-3 from step 4. This tells you that there are x mol in 1000cm3. You have to multiply this value by 1000 to get the "total" moles. Then divide this answer by the volume of FB2 used (which should be between 42.5 and 43.0 cm3)

Step 6: From step 5 you have the number of moles per dm3. To find the amount of grams per dm3, simply multiply your answer in step 5 by the Mr, to get the mass per dm3. In this case it will be:
concentration * 126

Hope this helps

thanks a lot
just one question in step 5 we multiply the conc found in step 4 with 1000?

[Ro1024]

are there titrations in paper 31??

[AS-Girl]

are there titrations in paper 31??

God only knows..

Reminder: No discussion of exams or predictions!!