Please help me with AP Chem

Test Preparation AP Test Preparation
1

<p>Just answer me thinking that I don’t know anything.</p>

<p>I have a few problems.</p>

<li><p>How do I know how many ions does a compound break into by just looking at the chemical formula of the compound?</p></li>
<li><p>If two compounds are mixed, how do I know which ions will combine and precipitate?</p></li>
<li><p>Most importantly, if the chemical formula is written in text, how do I know how many atoms of each element are present. For e.g. if Copper (II) Chloride is written, how do I figure out that it is CuCl?</p></li>
</ol>

<p>Please help me.</p>

2

<p>1) Generally, if something breaks up into ions in a solution, the number of each atom in the compound shows how many it breaks up into.</p>

<p>Eg - Ca(OH)2 -> Ca2+ + 2OH-</p>

<p>2) You just need to know which combination of ions precipitate, there are many solubility charts online. Here’s one:</p>

<p>[Solubility</a> chart - Wikipedia, the free encyclopedia](<a href=“http://en.wikipedia.org/wiki/Solubility_chart]Solubility”>Solubility chart - Wikipedia)</p>

<p>3) Cu(II) tells you that its a copper molecule with a charge of 2+</p>

<p>Similarly if it was Cu (I) it would only have +1 charge.</p>

<p>Since you know (or should know) that Cl has a charge of -1, it would take 2 Cl molecules to bond with one Cu (II)</p>

<p>Hence: CuCl2</p>

3

<p>Hey thanks.
For my 1st question.
What about it’s something like
C6H12O6, it doesn’t break at all then?
Also NaNO3 now this has 3 different atoms, but it breaks up only into two ions.
How do I know this?</p>

4

<p>Organic molecules usually don’t dissociate (AFAIK), so I dont think c6h12o6 does either. The thing about NaNO3 is that even thought It has 3 oxygens, nitrate is a polyatomic ion, which means you treat it as one ion. So NaNO3 breaks up into Na+ + NO3-. You can find a list of polyatomics online as well. This is really important. I recommend memorizing the important ones.</p>

5

<p>Is there a list of only important polyatomic ions</p>

6

<p>looks liek you wont do very well on the AP test. those things are some of the basics of regular chemistry.</p>

7

<p>yes- heres a good list- the top are the most common so you should really just know those and youll be fine</p>

<p>[Polyatomic</a> Ions](<a href=“http://home.earthlink.net/~ssbeaton/addlinfo/polyions.html]Polyatomic”>http://home.earthlink.net/~ssbeaton/addlinfo/polyions.html)</p>

8

<p>c6h12o6 dissolves, but doesn’t dissociate</p>

<p>ionic compounds and strong acids DO dissociate</p>