Chemistry coursework, identifying unknown chemicals

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Discussion Overview

The discussion revolves around strategies for identifying six unknown chemicals as part of a chemistry coursework assignment. Participants explore various testing methods and the limitations of available reagents, focusing on the identification of functional groups and the overall approach to the task.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant suggests starting with a litmus paper test to categorize the unknowns as acidic or alkaline, given the limited reagents available.
  • Another participant proposes conducting an iodoform test first to identify compounds with a CH3 group adjacent to a C=O group, expressing uncertainty about the effectiveness of this approach.
  • A third participant recommends creating a flow chart to outline the testing process, starting with the 2,4-dinitrophenylhydrazine (2-DNPH) test for carbonyl compounds.
  • There is a query about the reactivity of sodium hydrogen carbonate with compounds other than carboxylic acids, indicating a need for clarification on specific chemical reactions.
  • Two specific questions are raised regarding the pH of nitriles, particularly benzonitrile, and ethanamide, highlighting a gap in accessible information.

Areas of Agreement / Disagreement

Participants express differing opinions on the initial testing strategy, with some advocating for pH tests while others suggest starting with specific functional group tests. The discussion remains unresolved regarding the optimal approach to identifying the unknown chemicals.

Contextual Notes

Participants mention limitations in the number of tests that can be performed and the specific reagents available, which may affect the identification process. There is also a lack of consensus on the reactivity of certain compounds with sodium hydrogen carbonate.

Who May Find This Useful

This discussion may be useful for students engaged in chemistry coursework, particularly those working on identifying unknown substances and exploring various testing methodologies.

alias25
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i have to do the plan of my chemistry coursework by monday...

im having trouble with where to start..i have to identify 6 unknown chemicals. I am given a list with 8 chemicals that contains the name of 6 unknowns that i have and 2 extras.

im thinking of starting with a litmus paper test for alkaline/acidic. for all the chemicals and grouping them.
(we have limited reagents/test techniques we can use..
we have NaOH, H2SO4, NaHCO3, iodoform test, 2,4-dinitrophenylhydrazine, tollen's reagent. and water of course and bunsen burner)

any help would be appriciated thank you.
 
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im thinking i could do an iodoform test on them all firslty instead of acid/alkali to test for a CH3 group next to C=O group, is that a good move? bad?
because i, not sure where to go from saying these bunch of chemicals are acidic, i could then do an iodoform test on them...but that's silly if the other bunch of chemical, the alkaline ones have compounds with C=O next to CH3 as well, then i could do iodoform on them too.
i have to reduce the number of test i apply to these chemicals, so i can't just preform all tests on all chemicals.
 
I don't know about the PH test but I've done the general ID procedure several times - forgotten what it's called actually. My best advice would be to draw up a flow chart that runs over 2 odd pages.

I'll start you off: begin by adding 2-DNPH (to all of them until you get a positive) and that gives you either a POSITIVE or a NEGATIVE (as with any test). If its a POSITIVE you've got your carbonyl compounds, then continue your flow chart to differentiate between the carbonyl compounds. From the NEGATIVE route, go on to test for other compounds using their various tests.

Summing up:

1. Add 2-DNPH
If Positive -> Continue flow chart to differentiate between carbonyls
If Negative -> Begin other tests.
 
but my chemistry teacher advised to start with ph tests...but ill think about it, would you know if sodium hydrogen carbonate would react with anything other than carboxylic acid form that list?

1)can some one tell me the ph of nitriles in particular benzonitrile?

2)0and ethanamide? please i can't find anything by googling.
 
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