A student carries out an investigation on different plant extracts using paper chromatography. The experimental set-up he uses is shown below.
Where should he place the samples of plant extract?
On the pencil line
Below the pencil line in the solvent
Exactly 1 cm above the pencil line
Exactly 1 cm below the pencil line
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Paper chromatography was used to determine if a banned preservative, X, is present in four samples obtained from four different packaged foods labelled A, B, C and D.
The results of the analysis of the foodstuffs are shown in the diagram below.
Which foodstuff contains X?
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Four different dyes labelled P, Q, R and S produced the chromatograms as shown below.
Which dye has an Rf value of 0.7?
S only
R only
Both P and Q
None
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A student has been given a sample of an amino acid to analyse by chromatography. As part of the investigation the student will have to use a locating agent to make the colourless amino acid spots visible. The Rf value is then calculated to identify the amino acid.
Which row describes the correct steps?
|
How to add the locating agent |
How to identify the amino acid |
|
|
A |
Add to solvent |
Calculate the Rf |
|
B |
Spray on the chromatography paper before the experiment |
Compare the Rf value to that of known solvents |
|
C |
Spray on the surface of the solvent |
Perform the experiment again and compare the Rf values |
|
D |
Spray on the chromatogram |
Compare the Rf value to that of known amino acids |
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It is important that substances used in the synthesis of medicines are pure as impurities in these products can be detrimental to our health. Samples of pure and impure paracetamol were analysed using chromatography. The resulting chromatogram is shown below.
The impure sample of paracetamol was contaminated with one of the raw chemicals used during its synthesis.
What is the Rf value of the chemical?
0.70
0.75
0.65
0.85
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A mixture of sugars can be separated out by paper chromatography.
The student sprays the dried chromatogram with a locating agent.
Why is this used?
To help the sugars dissolve in the solvent
To stop the sugars reacting with each other
To form coloured spots with the sugars
To aid the separation of the mixture
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A student uses paper chromatography to find an Rf value for Fe3+(aq). The result is shown.
To make the spot containing Fe3+(aq) more visible, the paper is sprayed with aqueous sodium hydroxide so that a precipitate of iron(III) hydroxide forms.
Under the conditions of the experiment, the Rf value of Fe3+(aq) is given by …..1….. and the colour of the precipitate is …..2….. .
Which row correctly completes gaps 1 and 2?
|
|
gap 1 |
gap 2 |
|
A |
x/y |
green |
|
B |
x/y |
red-brown |
|
C |
y/x |
green |
|
D |
y/x |
red-brown |
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