Kinetics and Chemical Equilibrium

Running Head: KINETICS AND CHEMICAL EQUILIBRIUM 1
Kinetics and Chemical Equilibrium
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KINETICS AND CHEMICAL EQUILIBRIUM
1. A Laboratory experiment was conducted to illustrate the reaction rate of brass with boiling
acid and boiling base. Brass is an alloy of copper and zinc. The experimental set up was
done and the results were recorded within 12 hours. Graphs for mass of brass against
time for boiling acid and boiling base were drawn and after data was collected. Brass
reacts with both boiling acid and boiling base as shown in the graph. The only difference
is the rate of reaction. Two identical pieces of brass were placed in two different boiling
liquids for 12 hours. Using the provided information:
a. One similarity in the change in mass of the brass in both liquids is that Brass reacts with
both acid and base but the reaction rate with acid is more vigorous as compared to base.
b. Two ways in which the loss of mass shown in graph A is different from that shown in
graph B
i. In graph A, there is uniform mass loss meaning brass is reacting with the boiling acid
with the 12 hours while according to graph B, the mass loss stopped after some time
indicating no further reaction is taking place.
ii. Secondly, there is significant mass loss in graph A while the mass loss in graph B is
insignificant meaning reaction of brass with boiling base is a slow reaction or equilibrium
has been attained.
c. Three different safety precautions that are needed in doing this investigation
i. Acid solutions should be handled carefully as acids may be volatile. Safety glasses must
be worn.

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KINETICS AND CHEMICAL EQUILIBRIUM
ii. While diluting the acid, it’s the acid that needs to be poured into the water but not the
water being poured into the acid.
iii. Within the 12 hours, the temperatures of the two boiling liquids should be kept the same
for best results to be obtained.
2. Hydrochloric acid (HCL) reacts with Sodium Thiosulfate solution (NA2S2O3(aq)) to form a
white precipitate. The main objective of the experiment is to investigate the effect of
concentration on the rate of reaction between Hydrochloric acid and Sodium Thiosulfate
solution. Hydrochloric acid reacts with Sodium Thiosulfate to produce sulphur, sulphur
dioxide and water according to the below equation.
Na2S2O3(aq) + 2HCL S(s) +2NACL(aq) +SO2(g) +H2O(l)
The Sulphur dioxide being a highly soluble gas dissolves totally in the aqueous solution. Sulphur
since its insoluble remains in the mixture as a pale yellow or white precipitate and gives a milky
appearance which makes the solution milky and thus making the printed words on the paper to
disappear. Before the reaction starts, the printed words on the piece of paper are clearly visible
when viewed on top of the conical flask. However, as the reaction proceeds, sulphur precipitates
make the solution opaque and eventually the printed words disappear completely.
The time for the reaction varies with amount of reactants used. The time for the printed sheet to
completely disappear indicate how fast the reaction has taken place. Five tests were carried out
using different volumes of sodium thiosulfate, distilled water and hydrochloric acid as follows.