[SunnyBlu]

Can somebody please explain these concepts to me please? I've tried looking up examples online and in my book, but I feel like they are making what should be an easy concept, somewhat difficult to understand... 

[Borek]

Number of atoms of each element must be identical on both sides of each reaction equation.

Charge must be identical on both sides of each reaction equation.

Counting atoms is simple, counting charges is not much more complicated, just you have to remember about signs. H₂O molecule is neutral (net charge equals 0), mixture H⁺+OH^- is neutral too, as +1+(-1)=0.

[SunnyBlu]

Thanks! Okay, I think I am starting to understand a little more. I had this homework problem that just confused me more though, because in the answer I think the charges were unequal?
The Q was 'Write the charge balance for a solution that initially contains CsF and CaCO3'
And the A was [Cs+] + 2[Ca2+] + [H+] = [OH−] + [F−] + 2[CO32−] + [HCO3−]
I'm not sure how to know which elements to throw in... and aren't the charges 6 on the first side and -7 on the second?

[Borek]

Sorry, I misunderstood your question, I took it as pertaining to reaction equations, while you meant mass and charge balances for solution (or whatever).

But it is still not very complicated.

When you add any substance to solution, it may dissociate, react with other substances and so on. Mass balance tells the simple thing - amount of substance that was put into solution stays there, it may be just there in a different form. So, if you have added phosphoric acid to solution, it dissociates, but total number of moles of all dissociated forms doesn't change and equals amount of phosphoric acid introduced into solution.

Charge balance - all solutions are always neutral. That means amount of positive charge (in form of cations) equals amount of negative charge (in form of anions). However, you have to account of the fact that non all cations (anions) are charged equally - some have smaller charge (like +1 for Na⁺) some have higher charge (like +3 for Al³⁺). Those that carry more charge should be in a way counted more than once. Thus for example for MgCl² solution charge balance equation takes form 2[Mg²⁺] = [Cl^-] (Mg²⁺ counts as two).

And the A was [Cs+] + 2[Ca2+] + [H+] = [OH−] + [F−] + 2[CO32−] + [HCO3−]
I'm not sure how to know which elements to throw in... and aren't the charges 6 on the first side and -7 on the second?

Not elements - IONS. All ions that are present in the solution.

And no, there is no 6 & 7, but 5 on both sides.

[SunnyBlu]

Hmm okay, but how is the charge 5 on both sides? I mean, like you said in the case of MgCl, it would be 2[Mg2+]=[Cl-], why is this not a +4 charge for Mg and -1 for Cl?
(Sorry if I'm making this more complicated than it is..  )

[Borek]

You are not multiplying charges, you are multiplying charge by concentration.

Let's say you have 100 Mg²⁺ cations - how many +1 charges it is? 200, isn't it? 2 times number of cations. In terms of concentration - charge will be 2 times concentration of Mg²⁺.

[SunnyBlu]

Alrighty! Thanks so much for your *delete me* I really appreciate it!