Purity and separating mixtures

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Question 13

Medium

A chemist uses thin-layer chromatography (TLC) to investigate three different herbal drink samples ( $A$ , $B$ , and $C$ ) for the presence of organic acids.

Instead of a visual chromatogram, the chemist records the distance travelled by the solvent front and the individual substance spots:

Distance travelled by the solvent front = $cm8.0\text{ cm}$
Sample $A$ : spots at $cm3.6\text{ cm}$ and $cm6.4\text{ cm}$
Sample $B$ : a single spot at $cm3.6\text{ cm}$
Sample $C$ : spots at $cm1.2\text{ cm}$ , $cm4.8\text{ cm}$ , and $cm6.4\text{ cm}$

Explain what is meant by a pure substance in chemistry, and identify which sample ( $A$ , $B$ , or $C$ ) is a pure substance based on these chromatography results.

[2]

Calculate the $R_f$ value of the spot that is common to both Sample $A$ and Sample $C$ .

[2]

In another part of the investigation, the chemist determines the formulation of the herbal drink concentrate. An $g18.2\text{ g}$ sample of the concentrate contains:

Citric acid: $g2.4\text{ g}$
Malic acid: $g1.8\text{ g}$
Water: $g14.0\text{ g}$

Calculate the percentage of citric acid in this concentrate formulation. Give your answer to 2 significant figures.

[2]

Purity and separating mixtures

Question 13

Purity and separating mixtures Questions

Purity and separating mixtures

Question 13

Purity and separating mixtures Questions