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Question 5 Answer all questions [20 marks in total]
Gas chromatograph was used in monitoring the reduction of nitrobenzene. A calibration curve was given based the table.
\begin{tabular}{|c|c|c|c|}
\hline aniline/mM & \begin{tabular}{l}
dodecane/mM \\
b.p. $215^{\circ} \mathrm{C}$
\end{tabular} & \begin{tabular}{c}
Area \\
(aniline)
\end{tabular} & \begin{tabular}{c}
Area \\
(dodecane)
\end{tabular} \\
\hline 0.50 & 1.00 & 1503 & 5977 \\
\hline 0.75 & 1.00 & 2283 & 5843 \\
\hline 1.00 & 1.00 & 2987 & 5900 \\
\hline 1.25 & 1.00 & 3779 & 5905 \\
\hline 1.50 & 1.00 & 4500 & 5812 \\
\hline unknown & 1.00 & 3660 & 5783 \\
\hline
\end{tabular}
(a) Identify the peaks A, B and C. Justify your answer. (4 marks)
(b) Briefly explain how calibration curve was plotted from data of the table above. (5 marks)
(c) Calculate the unknown concentration in the table? Show your working. (4 marks)
(d) Suggest an extraction method for the separation of aniline from nitrobenzene. Justify your answer. ( 7 marks)
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Answer from Sia

Posted 2 months ago

Solution

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1 Answer

Peak A is aniline, Peak B is nitrobenzene, and Peak C is dodecane.

Key Concept

Gas chromatography separates compounds based on their boiling points, with lower boiling point compounds eluting first.

Explanation

Aniline has a lower boiling point than nitrobenzene, so it elutes first, followed by nitrobenzene. The internal standard typically has a different boiling point and elutes at a different time.

Solution

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2 Answer

The calibration curve was plotted using the area ratio of aniline to dodecane as the x-axis and the concentration ratio as the y-axis, with a line of best fit drawn through the data points.

Key Concept

Calibration curves are used to determine the relationship between instrument response and known concentrations.

Explanation

The curve allows for the determination of unknown concentrations based on the instrument's response, as represented by the peak areas.

Solution

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3 Answer

The unknown concentration of aniline is calculated by using the area ratio from the unknown sample in the calibration curve equation.

Key Concept

The calibration curve equation relates the area ratio to the concentration ratio, allowing for the determination of unknown concentrations.

Explanation

By inputting the area ratio of the unknown sample into the calibration curve equation, the concentration of aniline can be found.

Solution

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4 Answer

Liquid-liquid extraction is suggested for the separation of aniline from nitrobenzene, with pH adjustment to enhance separation.

Key Concept

Liquid-liquid extraction separates compounds based on their differential solubility in two immiscible liquids.

Explanation

Aniline's increased solubility in a basic aqueous phase compared to nitrobenzene allows for effective separation using liquid-liquid extraction.

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