confirm salts chem34

[Buffer Solution]

Well i got NH4 as the comon cation, while fe2 was the other cation. sulphate was in first one..
fb10 and 11 were alcohols and i messed up the ethalpy change question. i got ethlpy somewhere near 790kjmol.

 

[Garret]

hmm u got em right i think .. but why wudnt it be cr+3 ... when we left the solution .. it remained green for me and did not turn brown .. which means its wasnt Fe+2 .....
if only i had the presence of mind to add that k2cr2o7 agent to the solution to test if it was oxidized .. wed know for sure .

 

[sk8rdude]

Mine turned brown.. It was definitely Fe 2+....

 

[Garret]

argh crap....... oh well .. i still think il get 35 or 36.

 

[Supergirl]

I got Cr3+ aswell

 

[Supergirl]

I messed up the end of the enthalpy when we had to calculate some theoretical crap.
Couldn't do it :/

 

[Garret]

so ur solution didn't turn brown ??

I'd waited 5 mins while i was doing other questions and it hadn't turned brown for me at all so i was pretty sure it was Cr3+ ..... but as some are saying theirs did turn brown .. it would be iron :S ..

maybe they'll consider both fe+2 and Cr3+ .. hopefully .

 

[llppgg]

may i know wat u all wrote for obervation FB10 and FB11 with acidified potassium dichromate? thx...

 

[Garret]

turned green

 

[ashhadazam]

turned green.. FB 9 was ketone..
My enthalpy changae final was 25.56

 

[llppgg]

thx...urs turn green? i didnt get it yet i wrote it..

 

[ashhadazam]

lol they turned.. instantly.. One required bath tub other turned itself !!

And my silvber mirror was beautiful

 

[reeyn]

i wrote fe2+ coz when i pour the ppt on the tissue it clearly turned brown......
n orange turn green 4 observation PB10 and PB11 but i didn't get it though

 

[Garret]

hey thr was another trick question .. when theyd asked for error in single thermometer reading it was 0.5 *C ... but then they asked percentage error for the CHANGE in temperature of -12*C ..
as change is found by a - b sth ... the error would be 0.5 + 0.5 = 1 . i solved it this way .. got 8.3 % error .

maybe i just overthought it all .. howd u guys do it ?

 

[ashhadazam]

The mass was 0.1/5.6 * 100 !! i dunt remember how i did my opther part.. i think i did something like this ..

 

[ashhadazam]

What gradient u guyz got ?? I got 2.36 and 25.56 as my final enthalpy change..

 

[ashhadazam]

and what type of error did u people rite.. I wrote parallex error.. Because it doesnt affect the change in reading !!

 

[Garret]

wasnt the gradient negative ?! the change in temp was negative as the temp was dropping .. so readings would be -5 -10 -15 sth ... ur giving me a heart attack man .. sm1 plz confirm.

 

[ashhadazam]

The graph we had to plot was FALL in temperature against mass of NaHCO3... If u take fall as negative u are actually taking rise in temperature :O

 

[ashhadazam]

btw wt gradient and enthalpy values did u get ?