[CalculusCrazed]

Hello,

I was given the reactants and told to write out the products and assess if the reaction was likely to occur by indicating which side was favored. I worked this problem out but do not feel confident in the answer, but I cannot find another way to do it. What do you think?

Thanks,
CC

[CalculusCrazed]

Is this a more correct solution?

[voidSetup]

If CO₂ formed it would probably bubble out as a gas, not bear a negative charge. I think the question is asking if the bicarbonate is a strong enough base to pull the proton off of phenol so look at the pK_a's.

[orgopete]

Is this a more correct solution?

Sort of?

I suggest you use the following method. Write down the pKa of the acids in each reaction. The stronger the acid the weaker the base. The product will result in the weakest (conjugate) base. In this example, you should compare it with carbonic acid. Compare carbonic acid with phenol. Which is the strongest acid? The equilibrium will result in the conjugate base of that acid. As I had suggested in another post, go to http://www.curvedarrowpress.com/agocm/inside/sampler/sampler.html and click on the acid-base example.

[CalculusCrazed]

So I would then end up with a sodium ion instead of the weird thing I had up there?

[CalculusCrazed]

The reactants would be favored so this reaction wouldn't happen?

[voidSetup]

Yup need a stronger base like NaOH

[CalculusCrazed]

Yup need a stronger base like NaOH

So this is what is should look like?

I'm confused as to how this works. A stronger acid means that I will have a weak conjugate base, so that would mean that my phenol is a weak acid (pka= 10) and therefore gets a strong conjugate base? How do I know the strength of NaHCO3?

I get the fact that bases are proton acceptors and that acids are proton donors, but I guess I don't understand how we go about determining products. I don't see why one reaction is favorable over another. Would you mind helping me out?

Thanks,
CC

I'm sorry for all of the questions, I just want to get this straight.

[CalculusCrazed]

totally forgot my charges on the phenol(+) and HCO3(-)

[voidSetup]

No, I'm sorry.  You were correct before that the proton would be pulled off of the phenol, but the equilibrium favors the reactants so the reaction wouldn't happen.  I was saying that if you practically wanted to pull that proton off you would need a stronger base such as NaOH instead of NaHCO₃.

[orgopete]

I'm confused as to how this works. A stronger acid means that I will have a weak conjugate base, so that would mean that my phenol is a weak acid (pka= 10) and therefore gets a strong conjugate base? How do I know the strength of NaHCO3?

While one could have tables of base strengths, you will not find that to be the convention. However, it is simple to realize that they are related properties. The stronger the acid, the weaker the base. Therefore, if you look up the acidity in a pKa table, you can use that information to predict the relative basicity of the conjugate bases.

In this instance, just as stated, the pKa of phenol indicates it is a weaker acid than carbonic acid, therefore phenoxide will be a stronger base than bicarbonate (the stronger the acid, the weaker the base).

Just one additional consideration. One must be careful with carbonic and similar acids in that it has two values, carbonic acid and bicarbonate. Don't use the bicarbonate value for carbonic acid (this was not mistaken in this example).

[opsomath]

Other posts have done a pretty good job of addressing the OP's questions, but I just wanted to provide my Anion Stability List (tm) which I use to explain to my students how to figure out which of two materials will be a stronger base. You can use that information to figure out which side of an equilibrium will be favored: it's the one with the weaker base!

http://www.chemicalforums.com/index.php?topic=50971.msg189660#msg189660