For the weak acid ch3cooh (acetic acid) that is titrated with a strong base (naoh), what species (ions/molecules) are present in the solution at the stoichiometric point?

This is a strong base / week acid reaction.

NaOH + CH3COOH

The equilibrium of this reaction is very displaced to the right leading to the formation of the products

Na CH3COO + H2O

Na CH3COOH is a ionic compound which in solutionn will be as Na (+) and CH3COOH(-)

=> CH3COOH + NaOH = CH3 COO(-) + Na(+) + H2O

So, the predominant species in the solution are the ions Na(+) and CH3COO(-).

In general, in an strong base / weak acid titration, the predominant species present at the stoichiometric point will be the cation of the strong base (Na+ in this case) and the conjugate base of the weak acid (the anion of the weak acid, which is CH3COO- in this case).

The answer is predominantly Na(+) and CH3COO(-); predominantly because it is an equlibrium which means that the rectants will also br present.