Purity and separating mixtures

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Question 35

Medium

An analytical chemist uses thin-layer chromatography (TLC) to analyze three different plant-based dye extracts (Sample $X$ , Sample $Y$ , and Sample $Z$ ) for the presence of natural pigments.

Instead of viewing a visual chromatogram, the chemist records the distances travelled by the solvent front and the individual pigment spots:

Distance travelled by the solvent front = 12.0 cm
Sample $X$ : spots at 5.4 cm and 11.4 cm
Sample $Y$ : a single spot at 5.4 cm
Sample $Z$ : spots at 3.3 cm, 7.2 cm, and 11.4 cm

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

[3]

Calculate the $R_f\,$ value of the pigment spot that is common to both Sample $X\,$ and Sample $Z$ .

[2]

In another part of the investigation, the chemist determines the composition of the dye concentrate. A 22.5 g sample of the concentrate contains:

Active pigment: 2.2 g
Stabiliser: 3.5 g
Water: 16.8 g

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

[2]

Purity and separating mixtures

Question 35

Purity and separating mixtures Questions

Purity and separating mixtures

Question 35

Purity and separating mixtures Questions