Chromatography and Centrifugation - UNSOLVED PRACTICE SET

Q7. What is chromatography? Name the two phases involved and explain their roles briefly.

Q8. Explain the principle of centrifugation. Give two examples where centrifugation is used in everyday life or medical practice.

Q9. Your science teacher demonstrates paper chromatography using a mixture of red and blue ink. After running the experiment, you observe two distinct spots at different heights. Explain why the two colours separated.

Q10. Differentiate between the stationary phase and the mobile phase in chromatography. Why is it important that these two phases have different affinities for the components being separated?

Q11. Why is centrifugation preferred over filtration for separating blood plasma from blood cells? Explain the advantage in terms of time and efficiency.

Q12. A student performs chromatography on a leaf extract and observes several coloured bands. What does this indicate about the leaf extract? Name the different pigments that might be present.

Q13. Describe the process of paper chromatography with a labelled diagram. Explain how it can be used to separate the components of black ink. What factors affect the rate of movement of different components on the chromatography paper?

Q14. A doctor needs to separate blood into plasma and cellular components for a blood test. Explain how centrifugation achieves this separation. Include a description of the apparatus, the principle involved, and what happens to each component during the process.

Q15. "Chromatography and centrifugation are complementary separation techniques used in modern science." Discuss this statement by comparing the two techniques in terms of:
(i) principle,
(ii) types of mixtures they can separate,
(iii) applications in medicine and industry, and
(iv) advantages and limitations.

Q16. In a paper chromatography experiment, a mixture of three dyes — A, B, and C — is separated. The solvent front travels 12 cm from the baseline. The distances travelled by the dyes from the baseline are:

Dye A: 10 cm

Dye B: 6 cm

Dye C: 3 cm

(a) Calculate the Rf value for each dye.

(b) Which dye is most soluble in the solvent? Give a reason.

(c) If the experiment is repeated with a more polar solvent and Dye A now travels 11 cm, what does this tell you about the nature of Dye A?

(d) Why is the Rf value always less than 1?

Q17. A diagnostic laboratory centrifuges a blood sample at 3000 rpm for 10 minutes. The blood sample has a total volume of 10 mL.

(a) After centrifugation, the sample separates into three layers. Name these layers in order from top to bottom.

(b) If the plasma layer occupies 55% of the total volume, calculate the volume of plasma.

(c) The buffy coat (white blood cells and platelets) forms a thin layer of 0.5 mL. Calculate the volume of red blood cells.

(d) If the density of plasma is 1.03 g/mL, calculate the mass of plasma obtained.

(e) Why is it important for the laboratory technician to note the volume of each layer?

Q18. A food testing laboratory uses chromatography to detect artificial food colours in a sample of candy. The chromatogram shows four spots with the following Rf values: 0.85, 0.62, 0.45, and 0.30. The laboratory has reference standards with Rf values:

Tartrazine: 0.85

Sunset Yellow: 0.62

Ponceau 4R: 0.45

Brilliant Blue: 0.30

(a) Identify which food colours are present in the candy sample.

(b) If the candy sample weighs 5 g and the total mass of detected dyes is 0.05 g, calculate the percentage of artificial colours in the candy.

(c) The permissible limit for artificial colours in food is 0.1% by mass. Is this candy sample within the safe limit?

(d) Suggest one health concern associated with excessive consumption of artificial food colours.