Is H3PO4 a strong acid? (my text book says "there are relatively few strong acids: HCl, HBr, H2SO4m HNO3m H3PO4 are the most familiar...", it is but it's not in your list...) Also, is H2SO3 a weak acid?
For (NH4)2SO4, how can I get Kb for HSO4-? Which one should I use from the following values?
Acid Conjugate Base Ka1 Ka2 Ka3
H2SO4 HSO4- very large 1.0x10-2
Is this explanation of Na2SO4 salt wrong?
"Na2SO4 is an acid salt. The first ionization of H2SO4 is strong and NaOH is strong. =>neutral"
Also, would Na2CO3 be a basic salt? (there is no answer in my text )
(i)because HCO3- is weak
(ii)because H2CO3 is weak
Why (i) and (ii) both work as an explanation? Is there a case that (ii) will not work?
And would (NH3)2PO4 be a basic salt?
THANK YOU FOR YOUR TIME!
Hmmm. I have NEVER heard of H3PO4 being considered a strong acid. Every book I've ever seen has put it in the same class as acetic acid. If it was a strong acid, it would cause all sorts of problems in its use as a food additive. I also believe that H2SO3 is a "weak" acid.
1): You would use the Ka2 for HSO4-. Looking at the chart, it's giving you the Ka of all parts of sulfuric acid. Ka1 is VERY large because the H2SO4 easily gives up its first proton. (That's why it's a strong acid). HSO4- doesn't give it up nearly as easily so it's a weak acid with a the Ka being 1.0x10-2
(The Ka2 for H2SO4 is the Ka for the ion HSO4-). So if you go by my method of acid/base determination, you would look at the Ka of HSO4- and compare it to the Kb of NH4OH. If the Ka of HSO4- is greater than the Kb of NH4OH, your solution will be acidic. For your explanation, I'd go by something like this: "Na2SO4 is a basic salt because the SO4(2-) ion is the conjugate base of a weak acid (HSO4-), and the Na+ ion is a conjugate acid of a strong base (NaOH). Therefore in solution, at equillibrium, some of the SO4(2-) will pull a proton off of water which would form the stable HSO4- ion. The OH- ions will remain in solution, thus making it basic".
2): Na2CO3 would be a basic salt. For your reason you have to remember that when dealing with a multi-protic acid you only go back ONE step. So for the PO4(3-) ion, you would only go back to HPO4(-2), not H2PO4-, or H3PO4. For ANY conjugate base, when you are determining if it will form a basic or acidic solution you only go back one step. So the answer to this question would be '(i)because HCO3- is weak' since HCO3- is one step back from CO3(2-).
3): (NH3)2PO4. Hmmm. I did not know that salt existed. NH3 is a neutral molecule, and PO4 has a -3 charge. So something is definitely not right there.