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Topic: Writing the Formula of a Compound with Polyatomic Ions  (Read 4327 times)

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Offline Miss_Maple

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Writing the Formula of a Compound with Polyatomic Ions
« on: October 15, 2013, 05:05:39 AM »
Can somebody explain how to do this? I'm fairly confused on where all the ions are supposed to be. I comprehend you're supposed to balance them and make them equal -- but to order them correctly? How so?

I procrastinated all my thanksgiving Canadian weekend and it's 2:00am and I have much after this to catch up on as well. You uni/college students are incredible. I could never survive nights such as this.

Suppose somebody could use examples out of my books if needed, write the formulas:

lithium hydroxide
ammonium nitrate
lead (ii) perchlorate
potassium permanganate

Offline Borek

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Re: Writing the Formula of a Compound with Polyatomic Ions
« Reply #1 on: October 15, 2013, 05:42:17 AM »
You have to show your attempts at solving the question to receive help. This is a forum policy.

These are not difficult. For example the first - lithium hydroxide. What is a charge of lithium cation in compounds? What is a charge of hydroxide group? How many of each are needed for a neutral molecule? What are their symbols?
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Offline Miss_Maple

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Re: Writing the Formula of a Compound with Polyatomic Ions
« Reply #2 on: October 15, 2013, 06:57:09 AM »
Sorry, I'll remember that for the future. Thank you.

Unfortunately, I'm extremely new to this and I'm not wrapping my head around it ever so quickly, and I'd understand if I'm a tad early for this forum. Hopefully it's not too much frustration. Thank you for helping out.

So, lithium hydroxide -- Symbols: Li, OH-. The charge of the hydroxide group is negative (not sure if written name is supposed to be negative one or just the formula is like so), and the charge from lithium is positive, and what I'm comprehending from this is that the answer is LiOH.

Ammonium Nitrate -- Symbols: NH4+, NO3-. Ammonium is positive four, nitrate is negative three. I was told the positives and negatives had to be equal. I checked the answer here because I hadn't a clue, but I was guessing you would write NH4NO4 so they were equal..

Lead (II) Perchlorate -- Symbols: Pb, Clo4-, lead is multivalent because it has several charges: 2+ and 4+ but because of the roman numeral it's +2 in this case, there's the negative 4, and this is different from my last answer, but wouldn't it be something like Pb2ClO4? I have no idea how or why they work as such.

Potassium Permanganate -- Symbols: K, MnO4-, potassium is positive, permanganate group is negative 4. I'd figure it would be K4MnO4, for it to be equal..

Clearly missing a big picture with the balancing and/or charges. I'm completely lost. I'm quite shy to ask my instructor for help also. He's very wanting to get home after classes are finished and I find myself panicking when he's teaching individually because he's just fairly fast-paced.

Offline DrCMS

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Re: Writing the Formula of a Compound with Polyatomic Ions
« Reply #3 on: October 15, 2013, 07:47:34 AM »
Lithium Hydroxide is LiOH (Li+ and OH-)

But after that you've got them wrong because you are not looking at the polyatomic ion correctly.

ammonium nitrate
the ammonium ion has a central nitrogen with four hydrogens attached and has a charge of +1 so would be written as NH4+
the nitrate ion has 3 oxygens bonded to a nitogen and has a charge of -1[/sup] so would be written as NO3-
the charges need to balance so one positive ion and one negative give the neutral molecule NH4NO3  .

Can you do the other two yourself again having looked at these pages
http://en.wikipedia.org/wiki/Ammonium
http://en.wikipedia.org/wiki/Nitrate
http://en.wikipedia.org/wiki/Perchlorate
http://en.wikipedia.org/wiki/Permanganate


Offline Kate

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Re: Writing the Formula of a Compound with Polyatomic Ions
« Reply #4 on: October 15, 2013, 12:40:38 PM »
Just one correction DrCMS, NH4NO3 is not a molecule, it's a salt.

Offline Borek

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Re: Writing the Formula of a Compound with Polyatomic Ions
« Reply #5 on: October 15, 2013, 03:16:41 PM »
Just one correction DrCMS, NH4NO3 is not a molecule, it's a salt.

Does that mean that being shown spectrogram of gaseous NaCl you will call it a spectrum of salt?
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Offline Kate

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Re: Writing the Formula of a Compound with Polyatomic Ions
« Reply #6 on: October 15, 2013, 04:35:01 PM »
Does that mean that being shown spectrogram of gaseous NaCl you will call it a spectrum of salt?

Not sure what I'd call it, just saying that it isn't a molecule (or at least I thought so until you replied). :)

I mean, when people say NaCl is a salt, they're talking about the solid form of NaCl, I get that. Not sure if I totally understood your reply, sorry.

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