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Cisplatin, [Pt(NH3)2Cl2], is used as an anti-cancer drug - AQA - A-Level Chemistry - Question 4 - 2020 - Paper 3

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Cisplatin, [Pt(NH3)2Cl2], is used as an anti-cancer drug. Cisplatin works by causing the death of rapidly dividing cells. Name the process that is prevented by cis... show full transcript

Worked Solution & Example Answer:Cisplatin, [Pt(NH3)2Cl2], is used as an anti-cancer drug - AQA - A-Level Chemistry - Question 4 - 2020 - Paper 3

Step 1

Name the process that is prevented by cisplatin during cell division.

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Answer

The process that is prevented by cisplatin during cell division is DNA replication.

Step 2

Give the equation for this reaction.

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Answer

The equation for the reaction when cisplatin reacts with water to form a complex ion B can be represented as:

[Pt(NH3)2Cl2]+H2O[Pt(NH3)2(H2O)]2++Cl[Pt(NH_3)_2Cl_2] + H_2O \rightarrow [Pt(NH_3)_2(H_2O)]^{2+} + Cl^-

Step 3

Complete Figure 1 to show how the platinum complexes form a cross-link between the guanine nucleotides.

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Answer

In Figure 1, indicate the cross-link formation by drawing a bond (such as a dotted line) connecting the nitrogen atoms of the two guanine nucleotides with a platinum atom at the center.

Step 4

Explain how graphical methods can be used to process the measured results, to confirm that the reaction is first order.

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Answer

To confirm that the reaction is first order, we can plot the concentration of cisplatin (y-axis) against time (x-axis) to calculate the rate at different intervals. Tangents to the curve can be plotted, and if the rates are directly proportional to the concentrations of cisplatin, this would indicate a first-order reaction. Additionally, a plot of ln(concentration) against time should yield a straight line if the reaction is first order.

Step 5

Complete Table 1.

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Answer

The missing values for the rate constant in Table 1 can be filled based on the corresponding temperature values. For example:

  • For 293 K, the rate constant is 1.97 x 10^-6 s^-1, which results in ln k = -17.7.
  • Continue filling in the values accordingly.

Step 6

Calculate the activation energy, Ea, in kJ mol–1.

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Answer

To calculate the activation energy, you can use the slope of the ln k versus 1/T graph. From the graph (Figure 2), the gradient (m) is -Ea/R. Thus, rearranging gives Ea = -gradient × R.

Using the gas constant R = 8.31 J K–1 mol–1 and converting the gradient from the plot:

  • If gradient = -13.125, then:

Ea=(13.125)×8.31109.09 kJ mol1Ea = -(-13.125) \times 8.31 \approx 109.09 \text{ kJ mol}^{-1}

Therefore, the activation energy Ea is approximately 109 kJ mol–1.

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