what is the precipitate formed when HCl is added? I believe the answer is NaCl, but I am not sure and this precipitate only formed in the first NaOH extract, as precipitate was essentially nonexistent in the 2nd extract? Below is what was done in the experiment. Also, does the amount of precipitate in each tube indicate that all the acid impurity has been removed from the ether layer containing the unknown neutral compound? I believe precipitate formation means impurity is still present?
0.150g of an unknown mixture was placed in a centrifuge tube with 4 mL of ether. It was shook until the solid was completely dissolved. Then 2 mL of 1.0 M NaOH was added, tube shook, layers were left to separate, bottom (aqueous) layer was removed (1st NaOH extract). 2 mL more of 1.0 M NaOH were added to the tube, shook, layers separate, aqueous layer removed (2nd NaOH extract). Added 6 M HCl to each extract until each mixture was acidic. Precipitate formed at this point.
I don't think it is NaCl. If NaCl formed, wouldn't NaCl be formed each time NaOH + HCl came together. (Yes, NaCl forms but if it pptd after the first extract, it seems to me that it would ppt after all extractions.) I think this is what is happening.
Presumably you have an acidic compound and a neutral compound in the mixture.
The acid we might represent by RCOOH. So with the NaOH added, we form the sodium salt (which is soluble in water and the neutral compound is not). RCOOH goes to RCOONa. Then we separate the layers, add HCl to the RCOONa which forms the original acid and that is what is pptng. If you have all of the acid removed from the mixture, then the second extract contains no RCOONa and no ppt is formed when HCl is added.
Thank you very much.
Based on the information provided, the precipitate formed when HCl is added to the NaOH extract is indeed NaCl. NaCl is soluble in water but insoluble in organic solvents like ether, which is why it precipitates when HCl is added.
The fact that precipitate formation is observed in the first NaOH extract but essentially nonexistent in the second extract suggests that the acid impurity is mostly removed in the second extraction. This indicates that the impurity is predominantly present in the first NaOH extract.
The amount of precipitate formed in each tube does not necessarily indicate the complete removal of the acid impurity. It signifies that some acid impurity is removed, but it does not guarantee complete removal. Further steps such as additional extractions or purification techniques may be required to remove all traces of the impurity.
In this experiment, you started with an unknown mixture and wanted to separate and identify any acid impurities present. Let's break down the steps and address your questions:
1. Dissolution in ether: The unknown mixture was dissolved in 4 mL of ether by shaking until the solid completely dissolved. This step aimed to transfer the compounds into the organic (ether) phase.
2. NaOH extraction: Two separate additions of 2 mL of 1.0 M NaOH were made to the ether solution. Each time, shaking was done to ensure proper mixing, and then the layers (aqueous and organic) were allowed to separate. The bottom (aqueous) layer was removed after each extraction, resulting in two NaOH extracts. This step aims to transfer any acidic compounds from the organic phase into the aqueous phase.
3. Addition of HCl: Next, 6 M HCl was added to each NaOH extract. The purpose of adding HCl is to neutralize any remaining NaOH and convert it into its salt form (NaCl). However, it is important to note that HCl reacts with any free base present to form a precipitate of the corresponding salt.
Based on your description, a precipitate was formed when HCl was added. This indicates that there was an acid impurity present in the ether layer. The fact that precipitate formation was more prominent in the first NaOH extract suggests that the majority of the acid impurity was removed during the first extraction. The lesser amount of precipitate in the second extract indicates that a smaller amount of acid impurity was removed.
To address your specific question about the precipitate formed, it would indeed be NaCl. This is because HCl reacts with NaOH to form NaCl and water. The formation of NaCl as a precipitate confirms the presence of acid impurity in the organic layer.
In conclusion, the precipitate formation after adding HCl indicates the presence of an acid impurity in the unknown mixture. The amount of precipitate in each tube can give you an indication of the effectiveness of the NaOH extraction in removing acid impurities.