Thin-layer, column & gas chromatography

This question is about organic acids.

-Amino acids have the general formula RCH(NH₂)COOH.

Compound S is made of two -amino acids bonded together.

Compound S is hydrolysed into its component -amino acids.

The resulting mixture is analysed using TLC to produce a chromatogram:

The R group and the R_f value is shown for some -amino acids.

Determine the R_f values of the two -amino acids in the chromatogram.

Compound S has two possible structures.

Draw both of these structures.

This part is about compounds called -keto acids.

The equation shows the decomposition of a -keto acid.

Draw the structures of the organic products you would expect from the decomposition of the two other -keto acids below.

-Amino acids have the NH₂ group bonded to the carbon atom adjacent to the carboxylic acid group.

Suggest the difference between an -keto acid and a -keto acid.

A sample containing a mixture of 3 components, X, Y and Z, is analysed using gas chromatography.

The gas chromatogram below is obtained. The relative peak areas of X, Y and Z are included.

Which statement(s) is/are true?

1 The peak for component X shows the mass of one mole.

2 Component Y stays in the column for longer than component X.

3 Component Z consists of more than half of the sample.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about the analysis of organic compounds.

Determine the R_f value of propan-1-ol.

Show your working.

Write an equation for the alkaline hydrolysis of 1-bromopropane.

Show structures of organic compounds.

A student investigates the alkaline hydrolysis of 1-chloropropane using the same method as for 1-bromopropane.

Predict, with reasons, how the appearance of the reaction mixture in the chromatogram produced after 20 minutes would be different when 1-chloropropane is used instead of 1-bromopropane.

Suggest why propan-1-ol is run alongside the reaction mixture.

Write the formula of the species causing the colours after refluxing with acidified dichromate(VI

Green solution........

Orange solution........

* The student is provided with further information about compounds F– I.

• They all have the molecular formula C₅H₁₀O.

• One of the compounds is alicyclic.

• The other compounds are unbranched.

Use this further information and the student’s observations in Table 5.1 to answer the following.

• How do the observations provide evidence for the possible functional groups in compounds F– I ?

• Suggest a possible structure for each of the compounds F– I.

Show your reasoning.

A TLC chromatogram for two compounds is shown below.

What is the R_f value for the compound that is most strongly adsorbed onto the stationary phase?

A 0.25

B 0.33

C 0.69

D 0.78

Which statement(s) is/are correct for gas chromatography?

1 The components in a mixture can be identified from their retention time.

2 The relative peak areas give the proportions of components in a mixture.

3 Calibration curves are used to confirm the concentrations of components in a mixture.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about -amino acids, RCH(NH₂)COOH.

Table 17.1 shows the R groups in four amino acids.

In the boxes, draw the organic products for the reactions of serine shown below.

What is the R_f value of serine (ser) in solvent W?

Analyse the chromatograms to identify the unknown amino acid.

Explain your reasoning.

Name of unknown amino acid........

Explanation........

This question is about aromatic carboxylic acids and their derivatives.

The concentration of ester K in the cosmetic product is 9.13 × 10⁻² g dm⁻³.

Using the results, calculate the concentration, in mol dm⁻³, of ester M in the cosmetic product.

Give your answer to two significant figures.

concentration of ester M =........ mol dm⁻³