Chemistry Forum

Hi, I recently went back to college and Chemistry seems to be really giving me a run. I've been out of school for 20+ years and I'm struggling. Currently we are working on balancing equations, I understand the process and can get through the "easier" ones. The ones that I seem to struggle with the most involve subscripts and when to use parentheses. Is there a secret to this madness? Any tips? I swear I've watched every video online. I've been using the calculator tool provided to check my work and I can't seem to understand how it travels. I hope this makes sense.

Thank you

Give an example what you don't understand.

Ca + H₃PO₄

Supposed to identify type of reaction, full in the products and balance

The answer is Ca₃(PO₄)₂ + H₂

I cant figure out how/why the subscripts and parentheses appear.

Sorry if that doesn't make sense

Ca + H₃PO₄ => Ca₃(PO₄)₂ + H₂

So you see the Calciumphosphate contain 3 Ca, means you need them in the equation.

3 Ca + H₃PO₄ => Ca₃(PO₄)₂ + H₂

You also can see it contain 2 Phosphates, means you need 2 Phosphoric acid.

3 Ca + 2 H₃PO₄ => Ca₃(PO₄)₂ + H₂

At the end you count the hydrogen. On left side you have 6. On right side you need also 6, what means 3 H₂ will be developed

3 Ca + 2 H₃PO₄ => Ca₃(PO₄)₂ + 3 H₂

Finished.

In the answer how does Ca become Ca₃ ? That's where I'm unsure. Or why does PO₄ suddenly get parentheses?

I apologize if this seems like a silly question. We just started this equation stuff and have an exam on it already next week. I'm just trying to grasp the basics to at least pass

Calcium stand in the second group in the PSE. Means it is bivalent. Phosphate is an Anion what is trivalent. You can see it in Phosphoric acid it contain 3 H. H is monovalent.
The PO₄ as a fixed unit has to be in parenthesis therefore.
Calcium can connect 2 single bonds, Phosphate 3. Means you need 3 Calcium gives 6 bond and 2 Phosphates gives also 6 bond.
The Formula is Ca₃(PO₄)₂

Oh that's a lot to take in, I will keep trying. I truly appreciate the guidance. Thank you

I like very much how you explain about balancing and it’s very useful. Thanks !