1)when benzoic acid and quinine is dissolved in CH2Cl2 and added 2M NaOH, what is the organic layer and what is the aqueous layer?
a)and by adding another 2M NaoH to the organic layer, what is the new aqueous layer and organic layer?
b)from (1), if we add CH2Cl2 to the aqueous layer, what is the new organic layer and aqueous layer? and if we then add HCl to the aqueous layer, what is the product?
1) the aqueous layer will contain sodium salt of benzoic acid (sodium benzoate) while quinine will be dissolved in the organic layer.
a) new aqueous layer will still contain sodium benzoate, and the organic, quinine. the purpose of adding another 2M NaOH to the organic layer is to have any remaining unreacted benzoic acid to react with the additional NaOH added, which i think is to purify the organic layer so that it only contains the required component at the end, if you eventually need to carry out the recrystallisation of the quinine and benzoic acid.
b) same as part a), except that now you are getting any quinine that might've gone into the same flask as the aqueous phase and you need to have them separated...have the aqueous layer purified in the same manner as you did for the organic. lastly, the addition of HCl to the aqueous layer sees the recovery of (impure) benzoic acid in the form of white ppt, as well as sodium chloride.
[i noticed that this question has been asked some time ago but i think there may be others who would be searching for answers related to this question, hence for the following. my answers are based on the expt i did previously. hope this helps. pls do check with other sources too. thks :)]
additional notes:
- dichloromethane (CH2Cl2) is the organic solvent in which quinine dissolves; like dissolves like.
- NaOH (aq) reacts with benzoic acid to form sodium benzoate and water (acid-base reaction).
1) When benzoic acid and quinine are dissolved in CH2Cl2 and 2M NaOH is added, the organic layer and aqueous layer can be identified as follows:
- The organic layer: Benzoic acid is an organic compound that is insoluble in water but soluble in CH2Cl2. Therefore, benzoic acid will be present in the organic layer.
- The aqueous layer: Quinine, on the other hand, is an alkaloid that can be ionized in basic solutions like NaOH. So, when 2M NaOH is added, quinine will dissolve in the aqueous layer due to its ionization.
a) If another 2M NaOH is added to the organic layer:
- The new aqueous layer: Since benzoic acid is acidic, it can be deprotonated in basic solutions to form benzoate ions. Therefore, by adding another 2M NaOH to the organic layer, benzoic acid will react with NaOH to form sodium benzoate. As a result, the new aqueous layer will contain sodium benzoate.
- The organic layer: Quinine does not react with NaOH in this case, and since it was already present in the organic layer, it will remain in the same layer.
b) From the previous step (1), if CH2Cl2 is added to the aqueous layer:
- The new organic layer: CH2Cl2 is immiscible with water, so when it is added, it will form a separate layer. The new organic layer will contain CH2Cl2 and any dissolved organic compounds, such as sodium benzoate.
- The new aqueous layer: The aqueous layer will consist of water and any water-soluble compounds dissolved in it.
If HCl is then added to the aqueous layer:
- The product: HCl is an acid, and in the presence of sodium benzoate (from the previous step), it will react to form benzoic acid. So, the product of adding HCl to the aqueous layer will be benzoic acid dissolved in water.
To answer these questions, we need to understand the solubility properties of the given substances and the chemical reactions that occur.
1) When benzoic acid and quinine are dissolved in CH2Cl2 and 2M NaOH is added:
Benzoic acid is an organic acid and is soluble in organic solvents like CH2Cl2. When NaOH is added, it acts as a base and reacts with benzoic acid to form sodium benzoate, which is highly soluble in water. Thus, in this case:
- The organic layer will contain quinine (since it's not affected by NaOH), and benzoic acid (before it reacts with NaOH) dissolved in CH2Cl2.
- The aqueous layer will contain sodium benzoate formed from the reaction between NaOH and benzoic acid, dissolved in water.
a) Adding another 2M NaOH to the organic layer:
When additional NaOH is added to the organic layer, any remaining benzoic acid will react with NaOH to form more sodium benzoate, which is highly soluble in water. Therefore, in this case:
- The new aqueous layer will contain a larger amount of sodium benzoate dissolved in water.
- The organic layer will contain quinine dissolved in CH2Cl2, as it is not affected by NaOH.
b) Adding CH2Cl2 to the aqueous layer:
Since CH2Cl2 is an organic solvent, it will not mix with the aqueous layer. Instead, it will form a separate layer, with no significant change in the composition of either layer.
- The organic layer will still contain quinine dissolved in CH2Cl2.
- The aqueous layer will still contain sodium benzoate dissolved in water.
Adding HCl to the aqueous layer:
When HCl is added to the aqueous layer, it reacts with the sodium benzoate to regenerate benzoic acid. This reaction forms a new organic layer and results in the release of carbon dioxide gas.
- The new organic layer will contain quinine dissolved in CH2Cl2 and benzoic acid (formed from the reaction of HCl with sodium benzoate).
- The product of the reaction is carbon dioxide gas (CO2) which will be released.
Please note that the specific quantities and concentrations of the substances, as well as the temperature and reaction conditions, can influence the outcome of these processes.