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### Topic: calculation of buffer ph  (Read 5496 times)

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#### tantan

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##### calculation of buffer ph
« on: June 29, 2006, 05:54:24 AM »
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 ?
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

« Last Edit: July 01, 2006, 02:02:02 PM by Mitch »

#### Borek

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« Reply #1 on: June 29, 2006, 06:47:32 AM »
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
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### tantan

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« Reply #2 on: June 29, 2006, 09:12:50 AM »

i still didnt get how can i sove the calculation by the equation of buffer ph

??

#### Borek

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« Reply #3 on: June 29, 2006, 10:18:30 AM »
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.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### tantan

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« Reply #4 on: June 29, 2006, 12:13:30 PM »
what about the other problems ? anyone knows how to solve them ?

#### sdekivit

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##### Re: calculation of buffer ph
« Reply #5 on: July 02, 2006, 03:02:19 AM »
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)