Is The Salt (Nh4)2H2PO4 Acidic Or Basic? - Student Doctor Network

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You are using an out of date browser. It may not display this or other websites correctly.You should upgrade or use an alternative browser. Is the salt (Nh4)2H2PO4 acidic or basic?

• Thread starter Thread starter pacer
• Start date Start date Sep 11, 2014

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you. Status Not open for further replies. P

pacer

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Members do not see this ad. Is the salt (Nh4)2H2PO4 acidic or basic? NH4 is a conjugate acid of a weak base NH3 - so it also weak. HPO4 is a conjugate base of a weak acid (H2PO4) - so it should also be weak. The answer is that it is weakly basic. I am onfused. This is in reference to AAMC 5 Q23. The specific question asks for something else but I am asking in general as we need to determine if the salt is acidic or basic to answer the question and I am confused on how to do that since the ka and kb values are not given in the passage. Sort by date Sort by votes

Teleologist

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pacer said: NH4 is a conjugate acid of a weak base NH3 - so it also weak. Click to expand...

Not necessarily; consider the conjugate acid of hydrogen sulfate ion. The CA is sulfuric acid.

pacer said: HPO4 is a conjugate base of a weak acid (H2PO4) - so it should also be weak. Click to expand...

Bro why are you dropping charges like they're hot? Also, consider the conjugate base of water - a weak acid. The CB is hydroxide ion, and that's a strong base. Upvote 0 Downvote P

pacer

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I see your point with the other examples that the rule doesn't always stand. Can someone help explain with this particular salt, how would you go about determining if it is acidic or basic? Upvote 0 Downvote G

Gauss44

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I'm trying to remember if the Chad Video on this topic answers OP's question. Can anyone remember or check (if you currently have access to those)? Upvote 0 Downvote

justadream

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10+ Year Member Joined Apr 29, 2011 Messages 2,171 Reaction score 863 Points 5,246 @pacer From TBR , I think if both of the ions are weak after dissociation, you need to compare pKa/pKb values. Not 100% sure of the following logic works (@Teleologist - can you check?) but here goes: pKa of NH4+ is 9.25 pKb of HPO4 2- is 6.8 Since HPO4 2- is a stronger base than NH4+ is an acid, the overall solution is basic. Upvote 0 Downvote

Teleologist

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justadream said: @pacer From TBR , I think if both of the ions are weak after dissociation, you need to compare pKa/pKb values. Not 100% sure of the following logic works (@Teleologist - can you check?) but here goes: pKa of NH4+ is 9.25 pKb of HPO4 2- is 6.8 Since HPO4 2- is a stronger base than NH4+ is an acid, the overall solution is basic. Click to expand...

Good reasoning, but this is a difficult Q without a sense of acid/base strengths. Upvote 0 Downvote

justadream

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Teleologist said: Good reasoning, but this is a difficult Q without a sense of acid/base strengths. Click to expand...

Right, I had to google the pKa values. Something I would not have been able to do on the real MCAT. Upvote 0 Downvote

Ismet

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Closing thread, as it pertains to an AAMC full-length exam. Please read the sticky posted at the top of the forum regarding posting about AAMC FL questions: http://forums.studentdoctor.net/thr...ussing-aamc-questions-will-be-closed.1015927/ Upvote 0 Downvote Status Not open for further replies. Share: Facebook X Bluesky LinkedIn Reddit Pinterest Tumblr WhatsApp E-mail Share Link

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