PooyaH
07-10-2008, 11:19 PM
Which of the followwing pairs of compounds could be mixed to produce a buffer solution?
A. CH3NH3I and HI
B. CH3NH2 and CH3NH3I
C. CH3NH3I and NH4I
D. HI and NH4I
E. CH3NH2 and NH3
I got the right answer by eliminating the other choices, but it kinda took me a while to figure out which one is a weak base and it's conjugate acid!
Your thoughts...
osimsDDS
07-10-2008, 11:28 PM
Is the answer B???
Criteria for a buffer = weak acid/weak base with salt:
A) strong acid HI would not make a good buffer
C) doesnt make any sense, both are salts
D) HI again strong acid
E) no salt
therefore, answer must be B a weak base with its salt...
PooyaH
07-10-2008, 11:33 PM
Is the answer B???
Criteria for a buffer = weak acid/weak base with salt:
A) strong acid HI would not make a good buffer
C) doesnt make any sense, both are salts
D) HI again strong acid
E) no salt
therefore, answer must be B a weak base with its salt...
Yeah it's B and that's exactly how I got to the answer too...I didn't catch the weak base and its salt right away!
atlanta213
07-10-2008, 11:38 PM
how do you recognize the salt?
I know buffer contains weak base or acid + salt. However, I could not recognize the salt among choices while I determined weak base and strong acid.
wkawk2416
07-10-2008, 11:55 PM
yeah, how you know its salt of not.
osimsDDS
07-11-2008, 12:03 AM
CH3NH3+I-, just like Na+Cl-
PooyaH
07-11-2008, 12:04 AM
how do you recognize the salt?
I know buffer contains weak base or acid + salt. However, I could not recognize the salt among choices while I determined weak base and strong acid.
Just add the acid to it:
CH3NH2 + HI -> CH3NH3+I- (CH3NH3 has 1+ charge and I has 1- charge, making it a salt)
wkawk2416
07-11-2008, 12:35 AM
so it something forms ion, it can be considered as salt?
Thundercatz
07-11-2008, 12:39 AM
The Nitrogen on C also has 5 bonds. That is a dead giveaway that it isnt the answer!
klutzy1987
07-11-2008, 07:42 AM
Because there is an ionic bond between them. One is charged and the other is not. (Although i thought a salt was only a metal and non-metal hmm).
klutzy1987
07-11-2008, 07:44 AM
The Nitrogen on C also has 5 bonds. That is a dead giveaway that it isnt the answer!
Not true. The Iodine isnt covalently bonded to the nitrogen, it is ionic bonded to the entire (NH3CH3)+ group. It is the same as NH4I which is a common reagent. (remember the hoffman rearangement)