| Subject: Re: Chem Help |
Author:
Mr P
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Date Posted: 15:06:12 02/22/03 Sat
In reply to:
anonymous
's message, "Chem Help" on 20:10:50 02/20/03 Thu
Say Hey Anony,
Good for you! Many text authors mess this up!
Start with the acid H3PO4 Sorry about subscripts - we'll have to get used to the lack.
Phosphoric acid (note: -ic) is a poly protic acid. It has 3 acid hydrogens. Acid hydrogens are those that it will lose in aqueous solution. BUT it loses them one at a time.
H3PO4 ---> H+ + H2PO4(1-)
H2PO4(1-) ---> H+ + HPO4(2-)
HPO4(2-) ---> H+ + PO4(3-)
So in any phosphoric acid solution there are H+ ions, H2PO4(1-) ions, HPO4(2-) ions, and PO4(-) ions floating around. As well as the acid molecule itself H3PO4 which is soluble, but not a strong acid. It doesn't ionize 100% into all H+ and PO4(3-) ions.
The ions are named: dihydrogen phosphate, monohydrogen phosphate and phosphate.
So much for half of question 1.
Now, there is another acid, phosphorous acid, H3PO3. Unfortunately for the chemistry student, phosphorous acid is a diprotic acid. One of the hydrogens is not what we might call an acid hydrogen. In water, H3PO3 ionizes by losing Hs one at a time, bu only 2 Hs.
H3PO3 --> H+ + H2PO3(1-)
H2PO3(1-) --> H+ + HPO3(2-)
There IS no third step because the third H is bonded to the P rather than to one of the Os.
It seems acid Hs are H-O-P-, H-O-S-, even H-O-C-, but not H-P- or H-C-. The previous was supposed to indicate Hs bonded to Os bonded to P, S, C in phosphoric, sulfuric, or carbonic acids.
Sigh, so... to be safe, just don't pay much attention to phosphorous acid. It's really the only acid (that I know) that has one of those non-acid Hs. In all other cases (again, that I know) an acid will lose all of its Hs one at a time until it has none. The ions are therefore called trihydrogen, dihydrogen, monohydrogen, etc. Oh, btw, don't call the acid thrhydrogen phosphate or dihydrogen sulfate. We just call them phosphoric acid or sulfuric acid. Note, all -ic acids. hang on a while for the -ous acids.
Q2. Phew. Dioxide means two oxygens. carbon dioxide, has two Os, each bonded separately to the C. A peroxide is an O-O ion. The ion has two Os bonded to each other and is 2-. The Os of an oxide or dioxide are O(2-). The peroxide ion is O2(2-). Each O has an oxidation number of 1- (has gained on electron. The O(2-) has gained 2 electrons.
H2O2 is hydrogen peroxide, H-O-O-H. Water is H-O-H. You Are hitting the tough questions.
3. Another good one! Acetic acid is HCH3O2. One acid H. That is one H bonded to O H-O-C-, and 3 Hs bonded to C, aaaah, H-C-(H2)-. Sometimes we describe acetic acid as H3CC=OOH (3Hs bonded to a C bonded to a C double bonded to an O and that C is also bonded to an O bonded to an H.
Sorry I can't draw it here, but I'll try to find a good site that illustrates it and post it on myachem.
4. Yeah, the alums are a tough bunch. Ammonium aluminum sulfate would be NH4Al(SO4)2. Ammonium is 1+, aluminum is 3+, so it takes two SO4(2-) to balance the charges. Col? You can also have KAl(SO4)2 and NaAl(SO4)2. Got it?
5. in most cases, you can assume an aqueous solution. And in that solution, you will find that all soluble (note SOLUBLE)salts will exist as ions, and all strong acids will exist as ions. Weak acids will be written as molecules even though they will be partially ionized. Ask me about that in person.
6. Oh, you are hitting the beauties....
Mercury has two ion forms mercury (II) Hg(2+) and mercury(I), Hg2(2+). Mercury (I) is somewhat like peroxide in that it is Hg-Hg(2+) with each Hg having a charge of 1+ (each lost one electron). Hg(2+) the atom has lost two electrons. Best I can say is MEMORIZE, though it is a cop out. You won't have to know all the stuff above as long as you can write names and formulas and charges of ions.
7. Cupric ammonium phosphate, also called copper(II) ammonium phosphate. Total positive charge 3+, negative charge 3-.
You really asked the tough questions. you may get looks if you mention these to your classmates. They'll still be stumbling over sulfate, sulfide, sulfite. I'll be more than happy to talk in person. It'll take less time 9to read or write). But write any time.
JP
>
>Just a few questions for Mr. Paige...
>
>
>1. On the sheet titled "symbols, formulae, and charges
>of
>some common ions," why does it say HPO(sub3)(sup3-)?
>Isn't it supposed to be PO(sub3)(sup3-)? Also, is
>HPO(sub4)(sup2-) just "hydrogen phosphate" or
>"monohydrogen phosphate"?
>
>2. Also, what is the difference between dioxide and
>peroxide? Would H(sub2)O(sub2) be "dihydrogen dioxide"
>or "dihydrogen peroxide" or "hydrogen peroxide"?
>
>3. Also, is acetic acid HC(sub2)H(sub3)O(sub2) or
>H(sub4)C(sub2)O(sub2)?
>
>4. Also, is there such thing as "ammonium aluminum
>sulfate"? I can't figure out the formula for that
>one...
>
>5. Also, if the problem does not specify an aqueous
>solution should we assume and write it as an acid or
>just "hydrogen [anion]"?
>
>6. Also, does mercury (I) always have to be Hg(sub2)?
>Does that mean that mercury (I) will always appear as
>Hg(sub2) in any formula?
>
>7. Is CuNH(sub4)PO(sub4) "cupric ammonium phosphate"?
>
>Sorry to bother you... just had a few questions that I
>thought you might be able to resolve before I turn
>this in on Monday to Mr. Groce.
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