Question

Is sodium benzoate soluble in NaOH, NaHCO3

Answer 1

It's slightly soluble in an aqueous solution of
`NaHCO_(3)`, and almost insoluble in an aqueous solution of NaOH.

Step-by-step explanation:

Sodium benzoate comes from benzoic acid, which is a weak acid. It means that in an aqueous solution benzoic acid does not ionize easily to form the ions
`H_(3)O^(+)` and
`C_(7)H_(5)O_(2) ^(-)`

It also implies, according to the Le Châtelier's principle, that the ion
`C_(7)H_(5)O_(2)^(-)` tends to form the acid
`C_(7)H_(6) O_(2)` more easily. It can be seen in the following equation:

`C_(7)H_(6) O_(2)` ⇔
`C_(7)H_(5)O_(2)^(-)` +
`H_(3)O^(+)`

In an aqueous solution, the equilibrium shifts to the left, thus letting water dissolve sodium benzoate. But why? Because water in that case would produce enough
`H_(3)O^(+)` ions to facilitate the disolution of sodium benzoate. It's shown by its solubility in water at 15°C (62.78g/100mL, according to Wikipedia).

In contrast, the presence of NaOH or
`NaHCO_(3)`, both chemical species producing the
`OH^(-)` ions in aqueous solution, would make the equilibrium shift to the right because it would be a higher need of
`H_(3)O^(+)` ions to offset the presence of
`OH^(-)`.

However, the effect of NaOH is not the same due to
`NaHCO_(3)`, because the first is a strong base and the other is a weak one. Thereby it is reasonable to think that solubility of sodium benzoate is greater in water than in
`NaHCO_(3)` and NaOH.

Solubility in water > solubility in
`NaHCO_(3)`> solubility in NaOH.

Answer 2

It is water soluble so is also soluble in aqueous solutions of NaOH or NaHCO3.