Visualizing spots

Question: A colorless unknown substance is spotted on a TLC plate and developed in the correct solvent. The spots do not appear when visualization with a UV lamp or iodine vapors is attempted. What could you do to visualize the spots if the compound is the following:

My answer: Note that most organic functional groups can be made visible if they are charred by sulfuric acid.

A. An alkyl halide
My answer: Alkyl halides can be visualized if a dilute solution of silver nitrate is sprayed on the plates.. When exposed to light, dark spots will form on the plate.

B. A ketone
My answer: Colorless ketones can be colored by by making derivatives before spotting them on the plate. A derivative example can be preparation of 2,4-dinitrophenylhydrazone from ketones. You can also spray this reagent on the plate after the ketones have separated. Red and yellow spots will form where the compounds are located.

Please check these. Two more to come.

Sheryl



You need to get more opionions than mine but here are mine for what they are worth.
Why do you mention charring with H2SO4? Won't many organic chemicals char with H2SO4? And if it doesn't char what has it told you? And does that statement answer either of the two questions posed?
For the first one, I don't know if your procedure will work or not. Most alkyl halides do NOT have enough chloride ion (available as the ion) to react with AgNO3 and give a AgCl ppt. I assume that is what you are suggesting and the AgCl then does its thing and breaks down to Ag and Cl2 and the Ag is black. The other thing I am unsure about: AgNO3 will turn black, anyway, if left in the light long enough. All it takes is something to reduce enough silver ion to silver metal and the black is there. For the second one, ok EXCEPT that the question is what you can do to visualize the spot, not what you can do to make it separate into different spots. Therefore, spraying 2,4 DNPH is the answer you want. I think making the derivative BEFORE is superfluous to the question although it may be a perfectly good procedure to use.


I am beginning to see spots before my eyes.

  1. 👍
  2. 👎
  3. 👁

Respond to this Question

First Name

Your Response

Similar Questions

  1. social studies

    Drag the characteristics to the correct civilization. Characteristics may be used once or not at all. Korean civilization: developed on a peninsula Chinese civilization : developed on river valleys Japanese civilization: developed

  2. Chemistry

    ---This was the previous one--- Substances A, B, and C can all act as oxidizing agents. In solution, A is green, B is yellow, and C is red. In the reactions in which they participate, they are reduced to A-, B-, and C- ions, all

  3. College Chemistry

    please help! You are given an unknown, colorless, solution that may contain only one salt from the following set: NaA, NaB, NaC. In solution each salt dissociates completely into the Na+ ion and the anion A-, B-, or C-, whose

  4. 2nd year University BIOLOGY

    Why do we see pteridines but not ommochromes on a TLC plate?

  1. Concentration increase

    Question: What would happen to the Rf values of the pigments if you were to increase the relative concntration of acetone in the developing solvent? Note: The development solvent used was 70% hexane - 30% acetone. My answer:

  2. chemistry

    what is the density of an 84.7g sample of an unknown substance if the sample occupies 49.6cm3? what volume would be occupied by 7.75g of this same substance? PLEASE help need the answer tonight i have a test tomorrow i kind of not

  3. Chemistry

    The figure below is a heat curve for an unknown outerspace substance discovered by the Mars rover. By understanding the heat curve, scientists can make inferences about the composition of the planet. What is the temperature of

  4. Chemistry

    You and another student were each given an unknown compound. Both samples contained colorless material. You each used the same brand of commercially prepared TLC plate and developed the plates using the same solvent. Each of you

  1. Science

    13.)How can substance A and B be compared? Choose all that apply. A.)The particles of substance A have more energy than the particles of substance B.*** B.)The particles of substance A are more tightly held together than the

  2. TLC purity

    Question: A student spots an unknown sample on a TLC plate and develops it in dichloromethane solvent. Only one spot, for which the Rf value is 0.95, is observed. Does this indicate that the unknown material is a pure compound?

  3. Mobility and Rf

    We did a column chromatography then a TLC on extracted spinach pigments. Question: Why are the chlorophylls less mobile on column chromatography and why do they have lower Rf values than the carotenes? My answer: The chlorophylls

  4. More spots

    Question: A colorless unknown substance is spotted on a TLC plate and developed in the correct solvent. The spots do not appear when visualization with a UV lamp or iodine vapors is attempted. What could you do to visualize the

You can view more similar questions or ask a new question.