Why doesn't HCl form when you dissolve NaCl in water?
If you dissolve NaCl in water you will get some HCl molecules but there's definitely not going to be a significant concentration of HCl formed. 

The reaction that you propose - 

$\ce{Cl- + H2O -&gt; HCl + HO-}$ 

is highly thermodynamically unfavorable. 

We can ascertain this fact through consultation of any pKa/pKb table. In the equation above, the product acid (HCl) is a much (as in almost a trillion trillion times) stronger acid than water. 

Given that HCl is several trillion times stronger than water as a acid, then naturally, HCl will want to protonate hydroxide ion, a byproduct of HCl formation from chloride ion. This is ignoring the fact that hydroxide ion is also a strong base in water, so it has a high proton affinity in water. 

So even if the products were formed - again, very unfavorable from a thermodynamic standpoint because the reactant base and reactant acid are both so weak - then the products would certainly react with each other and form the reactants again, resulting in no net change in solution contents and pH. 



As a result, the reaction that you propose is more like this (except that the bottom/reverse arrow should be a lot bigger). 

$\ce{Cl- + H2O  &lt;&lt;=&gt; HCl + HO-}$