Weak acids?

This is really more of a conceptual question than anything.
(I realize how sad/odd it is that I'm asking conceptual questions about chemistry on a Maplestory fansite. Oh well.)

Now, here's a problem from my homework.

What volume of each of the following acids will react completely with 50.00mL of 0.200M NaOH?
a. 0.100M HCl
b. 0.150M HNO[SIZE="1"]3[/SIZE]
c. 0.200M HC[SIZE="1"]2[/SIZE]H[SIZE="1"]3[/SIZE]O[SIZE="1"]2[/SIZE]

I get how to do it and all, find the # of moles of OH- in the sodium hydroxide, set that equal to the # of moles of H+, and find how much volume of acid that equates to. Yada yada.

My question is this. According to the answer I get, it takes twice as much NaOH to neutralize the HC[SIZE="1"]2[/SIZE]H[SIZE="1"]3[/SIZE]O[SIZE="1"]2[/SIZE] than the HCl. Suppose the molar concentrations were the same, then it would take the same amount of NaOH for both.

However, acetic acid is a weak acid, so (I thought) it should require less base to neutralize it than for a strong acid like HCl. But that's not what the problem answer says.

So am I wrong, and weak acids and strong acids are actually equally capable of neutralizing a strong base (per mole), or is it something else I don't understand?

The strength of an acid affects how much of it disassociates in water. Here you are just looking for enough protons to cancel out all that hydronium.

What occurs (if I'm remembering my chemistry correctly) is that your OH ions from your NaOH will neutralise free protons in the solution. After that occurs, the acetic acid is also free to continue dissociating in the water, since the proton concentration has changed. Acetic acid will exist in x concentration in solution but only y% (which should be constant) of it will dissociate and add free protons.

You should understand more as you approach titration and learn of equilibrium constants etc.

If you are not taking the dissociation constants into account when you do your calculations, then it will appear that just as much base is needed to neutralize a weak base and a strong base on paper. However, in reality, I think it should take less base to neutralize a weak acid.

This is really more of a conceptual question than anything.
(I realize how sad/odd it is that I'm asking conceptual questions about chemistry on a Maplestory fansite. Oh well.)

Now, here's a problem from my homework.



I get how to do it and all, find the # of moles of OH- in the sodium hydroxide, set that equal to the # of moles of H+, and find how much volume of acid that equates to. Yada yada.

My question is this. According to the answer I get, it takes twice as much NaOH to neutralize the HC[SIZE="1"]2[/SIZE]H[SIZE="1"]3[/SIZE]O[SIZE="1"]2[/SIZE] than the HCl. Suppose the molar concentrations were the same, then it would take the same amount of NaOH for both.

However, acetic acid is a weak acid, so (I thought) it should require less base to neutralize it than for a strong acid like HCl. But that's not what the problem answer says.

So am I wrong, and weak acids and strong acids are actually equally capable of neutralizing a strong base (per mole), or is it something else I don't understand?

Everything deals with the pH curve. The pH does not significantly change until it is about to change from acidic to basic (weak acid). Thats why there is a sort of psuedo flat line, in which pH = pKA + log (A-/HA). Also you have to look at the mesure of Ka values of the acid versus the Kb of the base.

However in a strong acid, that point never happens because the acid and base quickly form a neutral salt.