Podcast
Questions and Answers
What is the Rf value of a spot that travels 6.2 cm, if the solvent front travels 10 cm?
What is the Rf value of a spot that travels 6.2 cm, if the solvent front travels 10 cm?
- 0.5
- 0.62 (correct)
- 1
- 1.61
Why is it important to use the same solvent in both the reference samples (E150 and E151) and the soft drink sample?
Why is it important to use the same solvent in both the reference samples (E150 and E151) and the soft drink sample?
- To ensure the Rf values can be compared accurately. (correct)
- To ensure all components travel at the same rate.
- To avoid any chemical reactions between the solvent and the dyes.
- To ensure the solvent front reaches the top of the paper at the same time.
What would happen if the solvent level was initially above the pencil line in the chromatography experiment?
What would happen if the solvent level was initially above the pencil line in the chromatography experiment?
- The chromatography paper would become too wet, leading to uneven separation.
- The spots would dissolve too quickly, leading to poor separation. (correct)
- The lid would not be able to seal properly, affecting the solvent evaporation rate.
- The solvent would evaporate too quickly, causing inaccurate results.
If the food coloring sample had an Rf value of 0.45, which dye would be suspected to be present in the soft drink?
If the food coloring sample had an Rf value of 0.45, which dye would be suspected to be present in the soft drink?
In this experiment, what is the purpose of using reference samples of E150 and E151?
In this experiment, what is the purpose of using reference samples of E150 and E151?
What is the purpose of using a pencil line in paper chromatography?
What is the purpose of using a pencil line in paper chromatography?
Why is it important to cover the glass tank with a lid during paper chromatography?
Why is it important to cover the glass tank with a lid during paper chromatography?
Which of these factors affects the distance a component travels in paper chromatography?
Which of these factors affects the distance a component travels in paper chromatography?
What is the purpose of using a locating agent in paper chromatography?
What is the purpose of using a locating agent in paper chromatography?
What happens to a component that is insoluble in the solvent used for paper chromatography?
What happens to a component that is insoluble in the solvent used for paper chromatography?
How can paper chromatography be used to identify a pure substance?
How can paper chromatography be used to identify a pure substance?
What is the Rf Value? (Retension factor value)
What is the Rf Value? (Retension factor value)
Why might two components overlap on a chromatogram?
Why might two components overlap on a chromatogram?
Flashcards
Rf value
Rf value
The ratio of the distance traveled by a spot to the distance traveled by the solvent, calculated as Rf = distance of spot / distance of solvent.
Baseline in chromatography
Baseline in chromatography
A pencil line drawn where samples are applied, ensuring ink does not interfere with results.
Solvent level in chromatography
Solvent level in chromatography
The solvent level must be below the pencil line to avoid dissolving the samples directly.
Purpose of a lid on the glass tank
Purpose of a lid on the glass tank
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Comparing Rf values
Comparing Rf values
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Paper Chromatography
Paper Chromatography
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Chromatogram
Chromatogram
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Pencil Line
Pencil Line
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Locating Agent
Locating Agent
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Solubility
Solubility
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Pure Substance
Pure Substance
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Impure Substance
Impure Substance
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Study Notes
Paper Chromatography
- Paper chromatography separates mixtures of soluble substances using a suitable solvent.
- Examples include separating dyes in ink.
- To separate purple ink:
- Draw a pencil line (baseline) about 2 cm from the end of the chromatography paper.
- Place a spot of purple ink on the pencil line using a capillary tube. Allow it to dry.
- Repeat applying the ink spot.
- Dyes suspected to be present in purple ink should also be placed on the pencil line.
- Place the chromatography paper in a glass tank containing a solvent, ensuring the solvent level is below the pencil line.
- Cover the tank and allow the solvent to rise.
- When the solvent level nears the top, remove the paper and let it dry.
- The resulting pattern (chromatogram) shows separated components.
Identifying Components
- The more soluble a component, the further it travels up the paper.
- A locating agent can reveal invisible spots (colourless spots) on the chromatogram.
- For example, amino acids are first separated by paper chromatography, then sprayed with ninhydrin to reveal spots as brown or purple colours
- In some cases, a component may be insoluble in the solvent, remaining on the baseline.
- Sometimes two components might overlap due to similar solubility, needing a different solvent for separation.
Purity of Substances (Mixtures)
- Paper chromatography helps to identify pure and impure substances.
- Pure substances have only one spot on the chromatogram.
- Impure substances (mixtures) have more than one spot.
Retention Factor (Rf) Value
- Rf values are calculated to identify components.
- Rf value = distance travelled by a spot / distance travelled by the solvent.
- Rf values are unitless and cannot be greater than 1.
Practical Considerations
- Pencil lines are used as ink in pens is soluble and can dissolve in the solvent and spread the spots around the paper, affecting the results.
- The solvent level should be kept below the baseline to prevent the spot from dissolving immediately before the solvent can separate components.
- Covering the glass tank prevents solvent evaporation, saturating the tank's inside with solvent vapour.
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