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# yet another chemistry question (aqa a2) Watch

1. hellloooooo, need some help please

i know its a pretty bog standard question, but i just cant get head or tail of it. its to do with acids and bases

Q1. calculate the pH of the diluted solution
you have 25cm3 of 0.1 moldm-3 HCl
you add to this 100cm3 of water

i calculated the pH at the start..
and its a flatline after that

2. pH = -log [H+]

HCl is a strong acid, so fully dissociates.
pH = -log [H+]
i did that for the start already
i just dont know what its asking afterwards because theyve given volumes
4. what is the new concentration? that'll let you work out the new pH
what is the new concentration? that'll let you work out the new pH
doesnt say..
or could i work out the mols of HCl..
then get the new conc. of the solution (conc=mols/vol)
then put that into pH = -log[H+]

the mols bit seems a bit out there though
6. Exactly, so find the moles of HCl initially, then find the new concentration with 125cm3 as the new volume. Now you have [HCl] which = [H+] so you can use pH = -log[H+]
7. (Original post by l4ith)
Exactly, so find the moles of HCl initially, then find the new concentration with 125cm3 as the new volume. Now you have [HCl] which = [H+] so you can use pH = -log[H+]
thanks
8. it gives you enough info to work out the new concentration, it's just a simple dilution.

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