Question

Writing equations of reactions:

1) Putting water & benzoic acid in a beaker. Add NaOH until benzoic acid dissolves. Write the equation of the reaction that has occurred, why did the product dissolve. Add HCl, write the equation of the reaction that has occurred, why did the product precipitate.

2) Put water & p-toluidine in beaker. Add HCl to dissolve p-toluidine. write the equation for the reaction that has occurred, why did the product dissolve? Add NaOH, write the equation for the reaction that has occurred, why did the product precipitate.

@Photon336

Answer 1

Maybe these will help me understand.... I found this online

If you first add NaOH
C6H5COOH + NaOH ---> C6H5COONa + H2O

then if you add HCl
C6H5COONa + HCl ----> C6H5COOH + NaCl

Answer 2

those figures explain it perfectly. sodium benzoate is ionic, remember ionic compounds when put in water are very soluble because they can break up and form ions, which can interact with water. remember like dissolves like.

water is polar right? so because of this the more polar a compound is the better the solubility it will have.

I wouldn't say it's entirely insoluble.

The primary reason benzoic acid dissolves only slightly in cold water is that, even though the carboxylic acid group is polar, the bulk of the benzoic acid molecule is non-polar (water is polar). It is only the carboxylic group that is polar.

okay so in the second picture when you add HCL right it protinates the carboxylate group like this.

HCL is such a strong acid that it there's almost entirely no HCL left. it all becomes H+ and Cl-

in that case the hydrogen's in solution would be picked up by benzoic acid.

I think it precipitates because don't forget we have Na+ ions in solution too as well as chlorine atoms too. It could also be that in addition to its low solubility, water is probably saturated because of the ions that exist in solution already, Na+ and Cl-.