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

[Pt(NH₃)₂Cl₂] + H₂O → [Pt(NH₃)₂(H₂O)Cl]⁺ + Cl⁻

In Figure 1, draw a line connecting the platinum atom to the nitrogen atoms (N) of the two guanine nucleotides to illustrate the cross-link. Label the connection as a coordination bond.

To confirm that the reaction is first order, one should plot the concentration of cisplatin against time on the y-axis. The slope of the tangent lines at various points provides the rate at which concentration changes. If the plot yields a straight line when plotting ln[concentration] vs. time, it indicates the reaction is first order.

The values for 1/T and ln k are filled in based on the given data. The rate constant, k, is calculated using the specified temperatures, resulting in ln k values that correspond to the respective temperatures.

To calculate the activation energy, Eₐ, use the Arrhenius equation. First, determine the gradient of the ln k vs. 1/T graph, which equals -Eₐ/R. The gradient is found to be approximately -13.125. Using the gas constant R = 8.31 J K⁻¹ mol⁻¹, the activation energy is calculated as follows:

$Eₐ = - ext{gradient} imes R = -(-13.125) imes 8.31$

Calculating this gives:

$Eₐ = 109.09 ext{ kJ mol}^{-1}$