Chemistry 3/4 2013 Thread

[teletubbies_95]

There's a great summary at the back of the Heinemann book in the appendices.

[teletubbies_95]

To standardise a solution of potassium permanganate of approximate concentration 0.2 mol L–1, an analyst took 25.00 mL
of the solution and made it up to 250.00 mL in a volumetric flask. He then measured out 1.117 g of oxalic acid crystals, and
made it up to 250.00 mL in another volumetric flask, using sulfuric acid of approximate concentration 0.2 mol L–1.
Next, 20.00 mL aliquots of the oxalic acid were titrated against the diluted potassium permanganate solution. The end point
was detected at the first permanent pink colour. The mean titre was found to be 18.95 mL.

1. equation= 2MnO4- + 5H2C4O4 +6H+ -----> 2Mn 2+ +10CO2 +8H20

I know this is an stupid question, but are why is there the use of sulfuric acid?
i'm getting confused with the use of "another volumetric flask".
sos. :0

[Homer]

wouldn't potassium permanganate be KMnO4?

[thushan]

wouldn't potassium permanganate be KMnO4?

Yup, but its the permanganate ion that's reacting. KMnO4 (aq) is really a mixture of K+ and MnO4- ions in solution.

teletubbies - the H2SO4 is to supply the H+ for the reaction.

[Homer]

hmm i get it, thanks toucan!

[teletubbies_95]

thanks toucan!
but can you explain something : I dont understand how to work out the questions as it says "using sulfuric acid  of 0.2 mol/L-".
so confused !

[brightsky]

thanks toucan!
but can you explain something : I dont understand how to work out the questions as it says "using sulfuric acid  of 0.2 mol/L-".
so confused !

What are you asked to find? Your original post only contained one question, which toucan answered.

[thushan]

thanks toucan!
but can you explain something : I dont understand how to work out the questions as it says "using sulfuric acid  of 0.2 mol/L-".
so confused !

Oh dw about that in this instance, you can assume the H+ is in excess, if anything, they mean dilute H2SO4.

[teletubbies_95]

@brightsky: it asks to find the concentration \
@toucan: okay , i get it ! thank you. finally understand.

[simba]

Yay! Chem tread!
Going to need all the help I can get next year in chem!
My teacher doesn't believe in teaching us by the vce -.- but I have the Heinemann book like most of you so yay! !
And we haven't been set any holiday homework, should I just do the first chapter or something? :/
Thanks!

[Mr Keshy]

Yay! Chem tread!
Going to need all the help I can get next year in chem!
My teacher doesn't believe in teaching us by the vce -.- but I have the Heinemann book like most of you so yay! !
And we haven't been set any holiday homework, should I just do the first chapter or something? :/
Thanks!

First chapter is a 20 minute max activity!

[teletubbies_95]

first chapter= quantitative and qualitiative stuff ,  important , but its pree short
do some questions from the first 4-5 chapters :0 its pree much year 11 revision.(i.e redox, stoich, volumetric analysis)
post as many questions !!

[Homer]

Should make like a whatsapp chem group! would be much easier to upload photos or questions

[teletubbies_95]

what's whatsapp?

[saba.ay]

what's whatsapp?

It's like KIK, It's an application on your phone where you can message people and send pictures. Not too sure if you can video/call.