Final answer:
The rate constant for the reaction between n-propyl bromide and thiosulphate ion is approximately 4.44 x 10-3.
Step-by-step explanation:
The given reaction is: n-propyl bromide + thiosulphate ion → (n-propyl thiosulphate) + bromine
The reaction is second-order, which means the rate of the reaction depends on the concentrations of both reactants. The rate law can be written as: rate = k[CzH-Br][S2O32-]
Using the given information, we can calculate the rate constant 'k'. The initial concentration of thiosulphate ion is 0.190 M, and it dropped to 0.0541 M after 18.5 min. Plugging these values into the rate law equation, we can solve for 'k', which comes out to be approximately 4.44 x 10-3.