Chemistry: Post your doubts here!

[aleezay]

Is Barium carbonate water soluble or insoluble? :/

 

[KurayamiKimmi]

umm hello ppl!
I wanna ask is it true dat the duration of d chem paper for tomorrow will be 2 hours?!
I mean I jst noticed dat 2011 and 2012 ques paper wz 2 hrs long... so any idea abt 2mrw' paper?!

best to practice and keep yourself in check for 1 hr and 45 mins , the 15 minutes, if they are given will come in handy for revising

 

[KurayamiKimmi]

Is Barium carbonate water soluble or insoluble? :/

insoluble

 

[Nab900]

wel its wriiten in chemistry book that in aqueous solutions Fe3+ is yellow..
we have to take the acidic and alakine conditions into consideration because they have specified it in the question, if u donot take the conditions into consideration u wil get stuck in the question because there are 2 different equations for O2 in th data booklet

OOHHHHHHHHKK!!!!! I did not see that!!!!!! they were asking in the question abt acidified also....

THANK YOU SO MUCH

 

[sumaiyarox:)]

okay, first off, find no of moles of NaOH → conc = moles/vol
moles of NaOH = 0.100 * (10 * 10^-3) = 0.001 moles

Moles of CH3CO2H = 0.250 * (10 * 10^-3) = 0.0025 moles
So, clearly, moles of CH3CO2H are in excess.
So, 0.001 moles of NaOH will react with 0.001 moles of CH3CO2H, leaving (0.0025-0.001) = 0.0015 moles of acid in the solution
Now, total volume of solution = 0.02 dm^3

So, conc of acid in soln = moles/vol
conc = 0.0015/0.02 = 0.075 mol/dm^3

Now, substiute values in pH = pKa + log ([salt]/[acid])
conc of salt → moles of salt = moles of NaOH
vol of soln = 0.02 dm^3
conc = 0.001/0.02 = 0.05 mol/dm^3

Hope u gt it!

what is d pH here?

 

[gary221]

what is d pH here?

4.6, i think.

 

[sumaiyarox:)]

4.6, i think.

how??

 

[sumaiyarox:)]

NMR is used to obtain the information about the number of hydrogen atoms and their chemical environment (to predict the structure of organic molecules ).
MASS SPECTROMETER is used to predict the relative atomic mass of the element,the different isotopes of the element and the relative abundance of the isotopes..
All chromatography techniques are used separate the different components in a copmound by using a mobile phase and a stationary phase..
but in each technique better mobile and stationary phases are used to make the results more reproducible and the separation more efficient.
TLC is similar to paper chromatography (PC) it has the same mobile phase (a polar solvent) as PC but a different stationary phase (slurry of silica or Al2O3),but the separation in TLC is better than that of PC because of the small size of the particles of stationary phase.
GLC uses an inert gas (N2 or Ne) as the mobile phase whereas stationary phase is inert porous diatomaceous rock which is packed in a glass column of narrow diameter (2mm), again the separation in GLC is better than TLC as the narrow diameter ensures the components to b in close contact with both stationary and moblie phase that increases the efficiency of separation... GLC is used to detect drugs in blood.
HPLC uses a high purity solvent as mobile phase that is puped under high pressures in the HPLC instrument , the stationary phase are the porous silica beads packed in a glass column of a narrow diameter, the results of HPLC is better than GLC... HPLC is used in the detection of explosive residues on the skin, it is used in the detection of pesticides in vegetables and fruits!

all dis asked in d papers?

 

[gary221]

all dis asked in d papers?

for knowledge, i guess.
i dont think this is asked.

pH = pKa + log([salt]/[acid])
pH = 4.76 + log(0.05/0.075)
solve to get pH = 4.6.

formula = pg 313 of coursebk

 

[sumaiyarox:)]

for knowledge, i guess.
i dont think this is asked.

pH = pKa + log([salt]/[acid])
pH = 4.76 + log(0.05/0.075)
solve to get pH = 4.6.

formula = pg 313 of coursebk

thnkkk uuu

 

[1357913579]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
4(C)
please someone help

 

[gary221]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
4(C)
please someone help

r u sure that's the right ppr?

 

[biba]

OOHHHHHHHHKK!!!!! I did not see that!!!!!! they were asking in the question abt acidified also....

THANK YOU SO MUCH

welcum

 

[biba]

all dis asked in d papers?

knowledge
but the uses or mobile and stationary phases of different chromatography techniques could be asked!

 

[sumaiyarox:)]

knowledge
but the uses or mobile and stationary phases of different chromatography techniques could be asked!

thnk uuu

 

[biba]

thnk uuu

u r welcum

 

[sumaiyarox:)]

u r welcum

 

[1357913579]

r u sure that's the right ppr?

really soory i meant 4(b)

 

[1357913579]

r u sure that's the right ppr?

in this question what iam confused is about why is b pb(so4) why not pb(so4)2 how in the exam would i know this?

 

[gary221]

in this question what iam confused is about why is b pb(so4) why not pb(so4)2 how in the exam would i know this?

pg 355 coursebk
the +2 oxidation state in lead compounds is much more stable than the +4 state.
So, it reduces to the +2 state ---> and forms PbSO4