Prelab #10 — Bromophenol Blue
Names (groups of 2) __________________________________
Lab section: M T W Th F
Work in groups of 2. Get permission ahead of time to work in a group
of 3.
Please show all work.
Reading Assignment:
Lab manual—Lab 10, including Background and Experimental sections.
Kinetics—Zumdahl, Chapter 15, especially p. 723: Integrated Rate Laws for
Reactions with More Than One Reactant.
1) Consider the reaction A + B AB.
a) Write the rate law for this reaction. Use “k” for the rate constant. Use
“m” and “n” to represent the order of reaction with respect to A and B,
respectively:
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b) In terms of m and n, what is the overall order of the reaction:
___________
c) When there are multiple reactants in a reaction, it can be difficult to
experimentally determine the reaction order of each reactant because
both concentrations are changing as a function of time. In a pseudo-first-
order reaction, one reactant is in extreme excess and its concentration
essentially remains constant during the reaction. This allows the rate law
to be simplified. Instead of using the rate constant, k, we use a pseudo
rate constant, k’, which combines both k and the concentration of the
reactant which remains constant. Thus, the rate law is written in terms of
only one reactant concentration. If B is in extreme excess, write the
simplified rate law, using the pseudo rate constant, k’:
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d) Write an expression for k’ in terms of k, [B], and n:
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e) The following exercise simulates what you will do with the data you
collect in this lab. In this exercise, the reaction above (A + B AB) is
performed twice. In the first trial, [B] = 1.0M. In the second trial, [B] =
2.0M. In both trials [B] is not changing measurably during the reaction.
However, [A] is measured as a function of time and its values are listed in
the data table below. This same data table (in an Excel spreadsheet) can
also be found in the lab manual.
Trial 1 Trial 2
[B] = 1.0M [B] = 2.0M
