Wednesday, November 25, 2009

Working with pH and ionization for AP Chem?

I need help with these sample probs for AP Chem so that I can figure out how this is done in order to do the rest myself. Im only asking cause Ive never had experience with these types of problems in chemistry.



1) A 0.5 molar solution of a weak acid was found to be 1% ionized. Calculate the pH of this solution.



2) The pH of a 0.2 molar solution of a weak base was found to be 12.5. Calculate the degree of ionization of this base.



3) What is the pH of a 0.5 molar solution of sodium hydroxide? ....Im guessing there is common info your supposed to know about this particular chemical?



Also, I understand how to calculate the H ion and OH ion concentrations from an integer (ie 1, etc) which would be 10^6 and 10^-13 for example. But how would you go about doing that with noninteger numbers such as 2.7, 6.1, 10.2. I suck at logs so any help would be appreciated



Working with pH and ionization for AP Chem?ireland



HA %26lt;-----%26gt; H+ + A-



initial concentration



0.5



at equilibrium



0.495 .. . . 0.005 . . 0.005



pH = - log 0.005 =2.3



pOH = 14 - 12.5 = 1.5



[OH-] = 10^-1.5 = 0.0316 M



0.0316 x 100 / 0.2 = 15.8 %



NaOH %26gt;%26gt; Na+ + OH-



[OH-] = 0.5 M



pOH = - log 0.5 = 0.30



pH = 14 - 0.30 = 13.7



You can use a calculator.



or if e.g. [H+] = 4.8 x 10^-13



pH = - log 4.8 x 10^-13 = - ( log 4.8 + log 10^-13) =



= - ( 0.68 - 13 ) = 12.32

No comments:

Post a Comment

 
computer repair