Blakhitman's chem questions thread!

[Blakhitman]

Ok, I suck at Chem.

I came to do H/W today and found I forgot some of the basics. So

1st question: Name the precipitate formed when aqueous solutions of the following compounds are mixed.

I don't want to know the answer (so I wont say what compounds), I just want to know how to go about answering it.

[kyzoo]

Use the solubility table to determine which product compounds will be soluble, and which are insoluble. The precipitates are the insoluble compounds.

[Blakhitman]

Oh yeah, thanks mate.

[Studyinghard]

Ok, I suck at Chem.

I came to do H/W today and found I forgot some of the basics. So

1st question: Name the precipitate formed when aqueous solutions of the following compounds are mixed.

I don't want to know the answer (so I wont say what compounds), I just want to know how to go about answering it.

Its quite simple actually. This is how my tutor taught me.

You firstly need to know how to use a solubility table.

http://intro.chem.okstate.edu/1515SP01/Database/Solub.html

For example:

AB + CD ----> AD + BC

AgNO₃(aq) + KCL(aq) ----> AgCl(s) + KNO₃

AB                           + CD            =   AD       +  BC

Now to see if it is soluble or not.
What you do is look at the D part and C part of your products.

AgCL - D part is CL . When you check the solubility table it shows that CL^- is soluble but there are a few exceptions that include Ag₊. Hence Ag⁺ amd Cl^- form AgCl (s), the precipitate.

KNO₃. The C part is NO₃.Looking at the solubility table, right away you can see that all NO₃^- are soluble, hence aqueous.

[Blakhitman]

Thanks A lot. Really appreciate.

Keep checking back, more where that came from! :p

[herzy]

i looked at that table, there are easier ways of trying to remember it.
for example, all period 1 elements (K, Na etc) will remain aqueous... try to find patterns, it'll help you remember

[kyzoo]

>.< This is what I can remember off by heart - so what I'm going to say might be wrong.

~ All period 1 (Alkali metals) metal compounds will be soluble
~ All halogen (Chlorine, Fluorine, Bromine, Iodine) compounds will be soluble, save for those containing Lead, Mercury or Silver
~ All ethanoate (CH3COO) ion compounds will be soluble
~ All ammonium (NH4) ion and nitrate (NO3) ion compounds will be soluble

~ All carbonate (CO2), hydroxide (OH), phosphate (PO4), and sulfide (S2) compounds will be insoluble save for when they are mixed with the above ions.

I missed out sulphate ion (SO4), its compounds are mainly soluble but I forgot what the exceptions are.

[stonecold]

You mean group one metals, not period.  Other than that kyzoo is spot on.

And I think Sulfate is insoluble with Barium, Calcium, Lead and something else.

[Blakhitman]

Thanks guys, I remember my methods teacher telling me how to remember now, something bout S.P.A.N.N.E.R, or was it S.P.A.N.N.A anyway I tried googling it but couldn't find anything on it and I can't remember what it means, anyone know this method?

[stonecold]

this is all i could find:

Do you know CASHn GIA

the mnemonic is:

C A S H n Gia

C is clorates, A is acetates, S is sulfates, H is halogens, n is Nitrates, and Gia is Group I A metals. ---> THESE ARE ALL SOLUBLE, except

for S: Ca, Ba, Sr.....just remember the tv network CBS
for H: Ca, Ba, Sr + Happy...whats happy? Hb Ag Pb ...mercury, silvr and lead...add a py to the end and all the first letters spell HAPPY

and if its not part of CASHnGIA...its insoluble.

it's somewhat average

[Blakhitman]

Oh thanks, that's pretty easy to memorise and quite clever!

[stonecold]

i just worked out what happy meant rofl.  that is quite clever!

....what are chlorate's and acetates?

i'm guessing anything with chlorine or acetic (ethanioc) acid in it?

[kyzoo]

Screw mnemonics. I just spent 20-30 minutes thinking about the solubility table and making notes on it, and then it just stuck.

What's the deal with OIL RIG anyway? There's a better way to remember it - The Law of Equivalent Trade (FMA  ), to gain something you must first lose something; but when you lose something you must gain something in return. In oxidation oxygen is gained, at the cost of electrons. In reduction oxygen is lost, and is compensated for by the gain of electrons.

[Blakhitman]

lmao kyzoo.

[Akirus]

Screw mnemonics. I just spent 20-30 minutes thinking about the solubility table and making notes on it, and then it just stuck.

What's the deal with OIL RIG anyway? There's a better way to remember it - The Law of Equivalent Trade (FMA  ), to gain something you must first lose something; but when you lose something you must gain something in return. In oxidation oxygen is gained, at the cost of electrons. In reduction oxygen is lost, and is compensated for by the gain of electrons.

Applying pseudo-scientific principles to reality... nice.