# Thread: When to use these formulas?

1. ## When to use these formulas?

When do I use CaVa = CbVb
and
n(titrated) = n(initial) - n(reacted) <------ I'm not sure if this is actually the formula, but yeah, I just wanna know when to use these two formulas

2. ## Re: When to use these formulas?

They're not really formulas, C=n/V is just number of moles per unit volume, what you wrote is just saying that if you don't change the number of moles, n=CV is constant, where C and V are not fixed.

2nd one is just common sense, if you have n moles initially, and m reacted, you have n-m moles remaining. In your case you just used the remaining moles in a titration.

3. ## Re: When to use these formulas?

Originally Posted by Librah
They're not really formulas, C=n/V is just number of moles per unit volume, what you wrote is just saying that if you don't change the number of moles, n=CV is constant, where C and V are not fixed.

2nd one is just common sense, if you have n moles initially, and m reacted, you have n-m moles remaining. In your case you just used the remaining moles in a titration.
So I won't need the first formula as long as I know C = n/v?

4. ## Re: When to use these formulas?

Originally Posted by BlueGas
So I won't need the first formula as long as I know C = n/v?
CaVa=CbVb is just using n=cv twice when your diluting solutions.

5. ## Re: When to use these formulas?

Originally Posted by Librah
CaVa=CbVb is just using n=cv twice when your diluting solutions.
And is the second formula I posted the correct one?

6. ## Re: When to use these formulas?

Originally Posted by BlueGas
When do I use CaVa = CbVb
and
n(titrated) = n(initial) - n(reacted) <------ I'm not sure if this is actually the formula, but yeah, I just wanna know when to use these two formulas
CaVa = CbVb needs to be used carefully. It assumes that a monoprotic acid (e.g. HCl) is reacting with a monoprotic base (e.g. NaOH) - or diprotic with diprotic, or triprotic with triprotic. If you have a diprotic acid, then it takes twice as many moles of a monoprotic base to neutralise it (e.g. H2SO4 with NaOH). I would strongly suggest that you calculate the number of moles as a specific step in solving these kinds of problems, and then refer back to a balanced equation to work out how many moles of the other reactant are needed to neutralise it.

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