1
Decomposition of Hypochlorite (Bleach)
2 OCl-(aq) 2 Cl-(aq) + O2(g)
The rate of a reaction may be measured by following the disappearance of reactants or
the appearance of products. The rate expression is as follows:
rate Reactants]
time
Products]
time
[ [
The rate of a reaction is affected by a number of different factors. Two of the factors that
will be studied in this experiment are reactant concentration and temperature.
The reaction is catalyzed by cobalt oxide formed when Co(NO3)2 solution is added to the
bleach. The reaction rate will be monitored by measuring the volume of water displaced
by the O2 gas produced. On day 1, various initial concentrations of the bleach will be
used to determine the reaction order by the “Method of Initial Rates”. The initial rate is
the linear slope of the plot of concentration vs time. The rate law is expressed by the
following equation:
rate = k[OCl-]x
On day 2, the activation energy, Ea, will be determined by elevating the temperature of
the reaction at a constant initial concentration of bleach and plotting of ln k vs 1/T.
PROCEDURE
Day 1 – Determination of reaction order.
1. Set-up the apparatus as shown in the Figure 1 on page 3. Fill the Florence flask with
water and insert the stopper assembly. Fill the tube connecting the flask and the
graduated cylinder by using a rubber pipet bulb, and then close the pinch clamp.
2. For each trial, measure 5 ml of Co(NO3)2 solution into a shell vial. The volumes of
bleach and water to be used are shown in the table below. Add the correct amount of
water and bleach into the Erlenmeyer flask. Tighten all stoppers and remove the pinch
clamp. If everything is tight, only a drop or two of water should drip into the cylinder.
Reaction Kinetics
Experiment
1
