Balancing Chemical Equations: Tips and Tricks for Frustrated Students

[Math Is Hard]

As you can tell, not my favorite subject. I was going along fine just tinkering with these things and working them out until I started trying to balance this one:

Ca₃(PO₄) + H₂SO₄ -> CaSO₄ + H₃PO₄

The coefficients I have tried so far are:

2Ca₃(PO₄) + 3H₂SO₄ -> 6CaSO₄ + 2H₃PO₄

so on LHS I have
6 Ca, 2 P, 20 O, 6 H, 3 S
and on RHS I have
6 Ca, 2 P, 32 O, 6 H, 6 S

(I think.. )

I wasn't sure if I needed to keep going and trying different or larger coefficients or if I have already gone wrong somewhere.

Also, if anyone has any tips for balancing these things I'd be glad to hear them. My teacher didn't give any formal procedures for working with these. Thanks.

 

[vsage]

Is there a coefficient on PO4 on the left side? Ca3 has a +6 charge in ion form..

Edit: The equation you posted I don't believe is balanceable. Trying to come up with a linear system to prove this.

Double edit: If there's a 2 subscript on the PO4, 1, 3, 3, 2 balances it left to right.

 

[Math Is Hard]

Hi vsage, thanks for responding. I am double checking the worksheet again... no, that's exactly how the equation appears.
Possibly the worksheet itself contains a typo?
I should mention that this is a class for "non-science majors", so the balancing should not be a difficult matter, I would assume...? Everything else has been beginner level.

 

[vsage]

Hi vsage, thanks for responding. I am double checking the worksheet again... no, that's exactly how the equation appears.
Possibly the worksheet itself contains a typo?
I should mention that this is a class for "non-science majors", so the balancing should not be a difficult matter, I would assume...? Everything else has been beginner level.

I am 100% confident there should be a 2 subscript on the PO4 on the left side. Every compound in the equation has to be electrically neutral and in order for Ca3(PO4) to be electrically neutral (PO4) must have a charge of -6. However if you look on the right side, there's H3(PO4) which has to be electrically neutral so I'd figure a P04 ion actually has a -3 charge.

Don't worry: I feel your pain. I hated AP chem so much last year. Studied my butt off and only got a B equivalent :( Shame on the sheet for having a typo.

Edit: It would not be unwise to wait for a second opinion though. I have been known to be wrong before but probably not on one of this difficulty (or rather facility)

 

[Math Is Hard]

Thank you for taking the time to look at this. I'll post back after I have class again and let you know what I found out!

 

[plover]

I second vsage. Even the notation that is there indicates that something is missing. I.e. why the parentheses in

Ca₃(PO₄)​

if the PO₄ isn't supposed to have a subscript. Plus a phosphate ion has charge -3. So:

Ca₃(PO₄)₂​

 

[Math Is Hard]

Something must be awry on the worksheet. I was hoping that maybe I was misunderstanding the meaning of the parenthesis, and that would explain it, but that doesn't seem to be the case.

 

[Math Is Hard]

while we're at it...

OK, while we're on the subject, let me ask this:
If you see parenthesis in a compound like Ba(OH)₂, why are those parentheses there?
I am treating it just as if it were written BaO₂H₂ when I do the balancing. Is this correct? I am assuming there are two hydrogen atoms and two oxygen atoms.
Thanks!

 

[TenaliRaman]

OH is a hydroxyl ion
Ba(OH)2 is basically a ionic bond with positive ion Ba and negative ion OH
so u see why OH is grouped together

I am treating it just as if it were written BaO2H2 when I do the balancing. Is this correct?

i don't see any problem with that ... ofcourse i cannot get pedantic abt it as i am not a chemist , yet seeing it as 2 oxygen and 2 hydrogen is fine ... still as far as the arrangement of ions is concerned , denoting the hydroxyl ion as (OH) is a must.

-- AI

 

[vsage]

I wouldn't get rid of the parenthesis because some polyatomic ions (like SO4) don't balance right if you break them up into their components because that ion forms covalent bonds to eliminate excessive negative charge. If you were to treat it as S1O4 then the overall charge would be -10 assuming all ions but in actuality when it's a polyatomic ion it's -2. I'd like to point out with hydroxide ions (OH-) the polyatomic ion's charge is equal to the sum of the indididual elements in ion form so you are not incorrect for that particular case but you can't always do that.

 

[Math Is Hard]

OK, thanks, y'all. I just wanted to make sure I was counting the atoms correctly and that the subscript 2 outside the parenthesis meant 2 Oxygen and 2 Hydrogen. It's the distribution of that 2 that I was concerned about.

 

[plover]

There are two separate issues here. In terms simply of the number of individual atoms involved in the reaction, (OH)₂ does correspond to 2 0 and 2 H. However, a group of atoms which forms a stable ion such as OH^- or PO₄^-3 or SO₄^-2 will act as a single unit in the reaction and should be thought of as such. This is especially true in cases such as vsage mentioned, where treating the atoms separately would suggest a misleading assessment of the charges involved.

 

[Math Is Hard]

What are the superscripts? Do those denote charges?

 

[vsage]

Well it depends on whether the sign is on the front or the back of the number. I think sign on back of a superscript is charge and sign on front is oxidation number but it's been a year since I took chem.

Edit yeah I wouldn't worry about it in any case you're not dealing with oxidation/reduction reactions for several weeks (if this semester)

 

[plover]

In my post, yes, they denote charges. And while I do recall seeing both SO₄^-2 and SO₄^2- as notations, I don't recall being taught that there was a difference between the two, which of course may just mean that I don't remember or may mean that the distinction is not used universally. A cursory googling did not clear this up. I suspect that if you ever need to treat them differently it will be made clear.

Sometimes the charge is indicated by a series of - or + instead, like this:

PO₄^---​

 

[SJC25]

vsage is right. But I am assuming ox/reduct is far in your future (next semester, if even then for a non major chem class).

All you need to remember is superscripts denote charges, subscripts denote numbers of, and there SHOULD have been a subscript after those parenthesis. Appears to be a simple typo to me.

Chemistry I know, Physics kicks my tail.

 

[Math Is Hard]

vsage is right. But I am assuming ox/reduct is far in your future (next semester, if even then for a non major chem class).

Actually, I hoping it's not in my future! I am definitely trying to get by with the minimum chem knowledge possible.

 

[Math Is Hard]

Update!

Yes! It was a typo!