Qualification > Sciences
CHEM AND BIO HELP AND TIPS HERE
nid404:
--- Quote from: sarasa on April 25, 2010, 03:05:00 pm ---Ok, If for example we used 25 cm3 of NaOH with concentration 0.1 mol/dm3 and it was neutralised by H2SO4 of concentration of 0.1 mol/dm3 then what is the volume of H2SO4 needed?
Repeat this with HCl having same concentration and also find its volume!!!!!!!
--- End quote ---
This is pure stoichiometry
Always write down equations to help you
2NaOH + H2SO4----> Na2SO4 + 2H2O
check the ratio of NaOH to H2SO4
2:1
Conc= mol/vol
moles=25/1000 X 0.1
=2.5X10-3
no of moles of H2SO4 = 2.5X10-3/ 2
=1.25X10sub]-3[/sub]
conc of H2SO4 used was also 0.1mol/dm3
vol of H2SO4[/sub= moles/conc= 1.25X10sub]-3/ 0.1=0.0125dm3=12.5cm3
frankly u don't have to do this....when u see the conc is the same....mole ratio=vol ratio
Second part
NaOH+ HCl= NaCl+H2O
Ratio is 1:1
so like i said don't bother...conc is same...vol of HCl used is 25cm3
If u further explanation...do ask
Hope this helps
Ghost Of Highbury:
NaOH H2SO4
Conc - 0.1mol/dm^3 Conc - 0.1mol/dm^3
Vol - 25cm^3 Vol - ?
2NaOH + H2SO4 --> Na2SO4 + 2H2O
Ratio - 2:1
No. Of Moles of NaOH - 25/1000 * 0.1 = 0.0025
There4 No. of Moles of H2SO4 = 0.00125
0.00125 = VOl. * 0.1
Vol = 0.00125/0.1 = 0.0125dm^3 = 12.5cm^3.
Ghost Of Highbury:
http://www.webchem.net/notes/Periodicity/titration_calcs.htm
Check this for examples and Revision.
sarasa:
Thank you very much....!
Now, sorry but I have another one :
Usually IGCSE questions ask to draw the structure of Nylon or Terylene so do we draw boxes and the Linkage like NHCO and COO or we have to know what the boxes represent?
nid404:
you can't know what the boxes represent until they tell you the name of the monomer...
so if they say simply to draw the structure, you just show the link and the box...but for polyamides, remember the boxes will be different...they have different monomer units
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