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This question is about methods of analysis - AQA - GCSE Chemistry - Question 5 - 2017 - Paper 1
Question 5
This question is about methods of analysis. A student wanted to compare the colours in two inks, A and B, using paper chromatography. 5 (a) (i) Describe a method t... show full transcript
Worked Solution & Example Answer:This question is about methods of analysis - AQA - GCSE Chemistry - Question 5 - 2017 - Paper 1
Step 1
Describe a method the student could use.
Answer
The student can use paper chromatography by following these steps:
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Preparation: The student should draw a horizontal line along a piece of chromatography paper, ensuring it is about 2 cm from the bottom. This line will be the baseline.
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Application of Inks: Dots of inks A and B are then applied on this line, spaced apart from each other.
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Solvent Placement: The bottom end of the paper should be placed in a solvent (such as water) without allowing the ink dots to touch the solvent initially.
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Chromatography Process: As the solvent rises up the paper by capillary action, it will carry the ink components upwards, resulting in their separation.
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Drying: The student should allow the ink to dry, preferably marking the positions of the separated colours with a pencil.
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Observation: Finally, a lid should be placed over the paper to prevent evaporation of the solvent.
Step 2
Compare the colours in the inks A and B.
Answer
From Figure 6:
- Ink A has 3 distinct colours and Ink B has 4 colours.
- Two of the colours are the same in both inks.
- However, there is one unique colour present in Ink A that is not found in Ink B, while Ink B has two colours that are not present in Ink A.
Step 3
Describe how gas chromatography separates substances in a mixture of compounds.
Answer
Gas chromatography (GC) separates substances based on their volatility and interactions with the stationary phase of the column. The process involves:
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Injection: A small volume of the sample mixture is injected into a heated gas chromatograph.
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Carrier Gas: This mixture is carried by an inert gas (the carrier gas) through a column packed with a solid or liquid stationary phase.
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Separation: As the components of the mixture travel through the column, they interact differently with the stationary phase, leading to varied retention times. Substances that interact less with the stationary phase will travel faster and exit the column earlier, while those that interact more will exit later.
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Detection: At the end of the column, a detector measures the different components as they exit, producing a chromatogram that shows the retention times and quantities.
Step 4
What information about each substance is given by the mass spectrometer?
Answer
A mass spectrometer provides the relative molecular mass (RFM) of each substance. It does this by ionizing the sample, accelerating the ions, and then separating them based on their mass-to-charge ratio (m/z). The result is a mass spectrum which displays peaks corresponding to different ions, allowing the determination of the relative formula mass and the identification of the substances present.