# Acids And Bases

1. Sep 25, 2004

### Jack16

Could You Help Me Out With This Question Please:

25.0 cm3 of a solution of 0.1M ethanoic acid is titrated with 0.1M sodium hydroxide.When sufficient alkali has been added to neutralise half of the acid,calculate

a)the concentration of ethanoic acid and ethanoate ions
b)the pH of the solution (Ka=1.7x10^-5 mol dm^-3)

Thanks Very Much!!!....

2. Sep 25, 2004

### chem_tr

Hello my friend,

First find C1*V1 by multiplying each other to learn the mole number. The same must be supplied in order to achieve neutral state. Where can you determine that half of acid is titrated? Mole numbers, of course.

Then write the equation, to see how many moles of ethanoate ions along with hydrogen ions are produced. Use the equilibrium constant, with omitting some values not needed really. If you can find the unknown value, you've already found the hydrogen concentration, and thus, pH value.

You'd better to solve this question by yourself, so I decided not to give the whole answer. But I'm here for your possible questions about it, with other members.

3. Sep 26, 2004

### poolwin2001

Remember the salt formed can hydrolise.This is a buffer solution(i.e. on further adition of acid or base,it will resist change in PH).
SO use

Henderson-Hasselbalch equation:
$$pH=pK_a+log\frac{[A^-]}{[HA]}$$

Last edited: Sep 26, 2004
4. Sep 28, 2004

### josephcollins

Hi guys,
I think that for part b there's no problem. I'm just having a hard time working out the values for concentration for part a. Would ethanoate ions mean CH3COO- or CH3COONa?The volume of acid is surely 12.5cm3?How about the rest of the concentrations and volumes, where would they come from?

5. Sep 28, 2004

### chem_tr

Hello, ethanoate ions are $$CH_3COO^-$$ only. If you add a sodium cation at the end of it, you'll get sodium ethanoate, which is essentially the same product, since sodium ethanoate also ionizes to ethanoate anion.