Benzenediazonium chloride, C₆H₅N₂Cl, decomposes in water as shown in the following equation. C₆H₅N₂Cl(aq) + H₂O(l) → C₆H₅OH(aq) + N₂(g) + HCl(aq) A solution of 0.0750 moldm⁻³ of C₆H₅N₂Cl(aq) decomposes at a constant temperature of 50°C. The volume of nitrogen gas, N₂(g), collected is recorded every 5 minutes for 45 minutes. Using this method, a student obtains the graph shown in Fig. 2.1. [Figure 2.1] Another student investigates the effect of changing the concentration of C₆H₅N₂Cl(aq) at 50°C. He measures the time taken to collect 0.0150 dm³ of N₂(g) and calculates the rate of N₂ production by dividing 0.0150 dm³ by the time taken. The results are shown in Table 2.1. Table 2.1 | concentration of C₆H₅N₂Cl(aq) / moldm⁻³ | time taken to collect 0.0150 dm³ of N₂/s | rate of N₂ production /dm³s⁻¹ | |---|---|---| | 0.500 | 21 | | | 0.400 | 33 | | | 0.300 | 48 | | | 0.200 | 64 | | | 0.100 | 122 | | C₆H₅N₂Cl is used in the manufacture of synthetic dyes. A student prepares a sample of the dye using the reaction scheme shown in Fig. 2.2. [Figure 2.2] In step 1, phenylamine, C₆H₅NH₂, is converted into C₆H₅N₂Cl. In step 2, C₆H₅N₂Cl is reacted with more C₆H₅NH₂ to produce the solid dye, which is then filtered.

1. (a)Draw a labelled diagram to show how the apparatus could be set up to carry out this experiment. [3][3]
2. (b)(i)On Fig. 2.1, draw a tangent to the curve at t = 0 mins. Calculate the initial rate of reaction in cm³ min⁻¹. initial rate of reaction = .............................................. cm³ min⁻¹ [2][2]
3. (b)(ii)Explain why the initial rate of reaction is calculated at t = 0 mins rather than dividing the total volume of gas produced by the time taken to produce it. [1][1]
4. (b)(iii)Describe how the curve in Fig. 2.1 would be different, if at all, if the atmospheric pressure increases. All other conditions stay the same. [1][1]
5. (b)(iv)On Fig. 2.1, draw a second curve to show the graph produced if the same volume of 0.0375 moldm⁻³ C₆H₅N₂Cl(aq) decomposes at a constant temperature of 50°C. All other conditions stay the same. [1][1]
6. (c)(i)Complete the table to calculate the values for the rate of N₂ production. Give your answers to three significant figures. [1][1]
7. (c)(ii)The reaction is first order and obeys the following rate equation. rate = k [C₆H₅N₂Cl] Explain how the data in Table 2.1 supports this statement. [1][1]
8. (c)(iii)State the dependent variable in this investigation. [1][1]
9. (c)(iv)The student wants to perform a similar experiment using 0.200 moldm⁻³ C₆H₅N₂Cl(aq). Describe how the student should make a standard solution of 100.0 cm³ of 0.200 mol dm⁻³ C₆H₅N₂Cl(aq) starting from a solution of 0.500 moldm⁻³ C₆H₅N₂Cl(aq). Give the name and size of any key apparatus which should be used and describe how the student should ensure the volume is exactly 100.0cm³. Write your answer using a series of numbered steps. [3][3]
10. (c)(v)Explain why (iv) must be carried out at a temperature below 5°C. [1][1]
11. (d)(i)The student's final yield was 52%. They had not spilled any reagents or products. Suggest two reasons why the student's yield was lower than 100%. Assume no errors were made in the measurement of any substances. reason 1: ................................................................................................................................................................ reason 2: ................................................................................................................................................................ [2][2]
12. (d)(ii)Explain why the solid dye should be dried before assessing the melting point. [1][1]

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