2 replies to this topic

[DragonX]

The homework board is gone

I'm wondering if you guys could help me out with a post-lab question:

Predict observations for the addition of the following solvents to sodium benzoate:
-Water
-Diethyl Ether
-6% aqueous HCl
-6% aqueous NaOH
-6% NaHCO3

Predict observations for the addition of the following solvents to an aqueous solution of sodium benzoate:
-6% aqueous HCl
-6% aqueous NaOH

Since this is a solubility lab, my thoughts were than sodium benzoate would dissolve in water, but not diethyl ether (since it is polar). Google seems to confirm this.
I further predicted that it would dissolve in the three acid/bases since HCl/NaOH/NaHCO3 are all polar, like with glucose which dissolved in water. However according to google, sodium benzoate doesn't "dissolve" in HCl but "reacts" with it to form benzoic acid

I'm not sure about the last additional tests either My guess would be that the aqueous solution of sodium benzoate is more polar that just sodium benzoate so it'll react with HCl and NaOH.. But then.. I'm not sure why they would put in this test since it already reacts/dissolves in it without being in solution.

Edited by Ken, 26 May 2010 - 01:47 PM.

[tat87]

Maybe they want you to observe the rate of reaction on the second part, as compared to non-aqueous sodium benzoate? Maybe since it is aqueous, the surface area of the compound is much larger, thus a faster rxn rate?

[DragonX]

I don't think so since this question was given after the lab was completed as a post-lab question .

I think I figured it out though.. this is what I ended up putting:

Sodium benzoate will disolve in both the HCl and NaOH aqueous solutions since it is a salt, and salts dissolve in aqueous solutions.

Likewise, it will dissolve when added to water to make a sodium benzoate aqueous solutionsolution. When this happens, the sodium cation is separated and the aqueous soltuion will react with the HCl aqueous solution but not with NaOH aqueous solution since sodium benzoate is a base.

Thank you for your help though