[dkssudgktpdy]

I am having trouble assigning which one is strong and weak. Please help me out.

CH3C triple bond CH   +  OH-     -><-(equilibrium)  CH3C triple bond C-  + H2O

So my note says,
CH3C triple bond CH is a weak acid  AND  CH3C triple bond C- is a strong conjugate base. 
WHY?? I'd like to know  reasons behind this.

Also, Why is this equilibrium shifts towards left? Wouldn't it stay in the middle because acids on both sides are strong? I thought the equilibrium would shift towards weak acid/base.

Thanks for your inputs.

[fledarmus]

Look up the pKa for methylacetylene and water. Although both are weak acids, one is far weaker than the other...

[dkssudgktpdy]

what if you are not given pKa values?

[Nosterius]

Find them.

There are plenty of pka tables on the internet. Check for Evan's pka table for exemple.

[fledarmus]

Then you need to develop a good feel for the relative acidities and basicities of a lot of functional groups. You can't memorize the pKa for every compound, but you need to at least have some feel for the groups.

In your case, you are looking at an acetylenic hydrogen compared to a hydroxy hydrogen. Although an acetylenic hydrogen is acidic compared to, say, an alkyl or alkenyl hydrogen, that is far far less acidic than a hydrogen attached to an oxygen, nitrogen, sulfur, phosphorus, or almost anything else except a metal. Carbons really do not want to lose their hydrogens to gain a negative charge, while oxygen is pretty okay with it. Pulling a proton from nitrogen isn't as easy as pulling it from oxygen, but still far easier than pulling it from carbon. And so on. As you learn about new functional groups, you need to get some idea of what effect they will have on the acidity of attached or neighboring hydrogens.

[dkssudgktpdy]

thanks !