Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tantan on June 29, 2006, 05:54:24 AM
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hello i have my biochemistry final tomorrow and i need your help guys ...
if some 1 can help me live online its better for me, my msn address is : atanas_zaher@hotmail.com
we can chat and u can help me,
first problem : calculation of buffer ph
** 0.81M NH4Cl , with 0.35M NH3 ,(Kb of NH3 is 1.8*10-5 ) (1.8* ten to the power of minus five ) - what is the ph of the buffer
1)8.89
2)8.82
3)9.62
4)5.11
one of these answers , i just dont know how to do it :( :'(
the second problem is :
*** an ionic crystal of 2 grams, in 400 grams water has a freezing point of 0.308c (celzius) ,The molal freezing point of water is 1.86c (celzius) , its known that this ionic crystal dissociates into 2 electrolytes , what is the molar mass ?
1)40
2)60
3)80
4)120
5)140
and last question i have is not calculation :
what are the minor bases of RNA ?
1) 6-Methyl Adenine
2) 7-Methyl Guanine
3) 2-Methyl Cytosine
4) 2-N- Methyl Guanin
5) HydroxyLamine
Thanks So Much For Your Help And COoperation :(
atanas :)
atanas_zaher@hotmail.com
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first problem : calculation of buffer ph
** 0.81M NH4Cl , with 0.35M NH3 ,(Kb of NH3 is 1.8*10-5 ) (1.8* ten to the power of minus five ) - what is the ph of the buffer
Calculation of buffer pH (http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch)
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i still didnt get how can i sove the calculation by the equation of buffer ph
??
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You have Henderson-Hasselbalch equation at the link provided, you have concentration of the acid and conjugated base given in the question, you have Kb value - all you have to do is to enter these values into the equation.
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what about the other problems ? anyone knows how to solve them ?
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the second one is freezingpoint depression
delta delta Tf = -Kf * m * i
(delta Tf = freezingpoint depression, Kf = molal freezingpoint depression constant, m = molality of solute and i = amount ions after solution / moles of solute before solution)
now fill in this formula and you will find your answer.