Question

Choose the best laboratory technique to use in each of the following situations. Each answer should only be used once.

1. You want to conform the identity of a solid organic molecule you have extracted from a flower petal. You do not have a standard sample of this material to compare it to but you do know the name of this molecule and have reference books you can use to look up physical properties of organic molecules. 2. Separation of two liquids in a volume of 76 mL that are mixed together is your goal. You plan on recovering the liquids after separation to run further tests on their properties. You know that the boiling point of liquid A is 86oC and the boiling point of liquid B is 112oC. 3. You are planning to carry out a reaction of two solids dissolved in water and know that it will require heating to 90oC for 3-4 hours. What technique can you use to accomplish this? 4. You carried out a microscale organic synthesis reaction and suspect that you have a mixture of products in your 0.4 mL sample. All your suspected products have boiling points over 280oC but different polarities. You would like to check to see if your sample is a mixture and what the relative concentrations of the different components of the mixture are without using all of your product. What technique would work best?    5. You work in a quality analysis laboratory and are asked to determine if a 0.2 mLsample of gasoline has any heptane (boiling point 98.4oC) in it. You have reference sample of all liquid alkanes commonly present in gasoline to use for comparison. What technique would work best for separating the components of gasoline and identifying any heptane present? 6. You have a sample of a solid pigment extract from a blue flower petal that you want to analyze to see if the color comes from one pigment molecule or a mixture. You know these pigment molecules are normally large and have high boiling points but that they often have enough differences in functional groups to make their polarities different. Your laboratory's HPLC ihas been sent out for repair? What other technique would be best to use for this? A. melting point determination B. distillation C. reflux D. high pressure liquid chromatagraphy E. gas chromatography F. thin layer chromatography

Answer 1

A. melting point determination:is the way to test if the substance is pure.

B. distillation : separation process of component from mixture of liquid on the basic of relative volatility (diffrerence in B.P)

C. reflux: used in chemistry to supply energy for reaction for long period .in this process vapour condense is fed back to column from where it originate

D. high pressure liquid chromatagraphy:it is use to separate ,identify & quantify component in mixture

E. gas chromatography: it is use to separate & analyse compound which can be vapourise without decomposition.it can be use to prepare pure compound.

F. thin layer chromatography:use to separate non volatile mixtures.

Situation ---->technique

1 melting point determination

as we know molecule name & can refer physical properties from reference book. so we can confirm the presence of compound.

2 B.Distillation

as we have boiling point difference is much larger .& by distillation we can get both compound separated so we can run futher test.

3 C.Reflux

as we know reflux is also use for heating .The purpose of heating on given temp for 3-4 hr can be accomplished by this process.

4 D.HPLC

as for microcsale synthesis we have to check relative conc . of sample.component of mixture without using all of sample.

5 E.gas chromatography

as compound can be vaporised without decomposition .

6 F.thinlayer chromatography

this is best method as HPLC is not working & compound have different polarities