Ocean County College

CHEM 182

Abstract:
These experiments were designed to be able to determine the chemical equilibrium of a mixture
based off observing color change when two reactants are combined, and no more change
happens. These experiments tested different mixtures as well as varying stresses (temperature) to
be able to use Le Chatelier’s Principle to determine the chemical system shift. The principle
states that a system in equilibrium will shift in favor of reducing the stress. Based off these
changes the system shift was able to be determined knowing if the shift was toward products
(right) or reactants (left). In the case of dichromate increasing temperature will shift the system
towards the right in favor of the products and decreasing the temperature shifts the system in
favor of the reactants (left). Overall, the purpose of these experiments were achieved in being
able to observe changes to determine equilibrium and chemical system shift.
Introduction and Background:
This report discusses the experiments and observations performed to determine chemical
equilibrium, which is when the concentration of reactants and products are constant and have no
more changes. Calculations where than used to be able to determine the equilibrium constant
which is the value of the reaction quotient (the value that is calculated from the reactants and
products in a equilibrium expression) at the chemical equilibrium. Once this value is determined
it can be used in conjunction with Le Chatelier’s Principle, which states when a stress
(disturbance either from change in volume, temperature or pressure) applied at equilibrium to a
chemical system the system will shift to minimize the stress. For example, if there was an
increase in the concentration of the reactants the chemical system would shift towards the right
(towards products) to return to equilibrium. The experiments found the chemical equilibrium of
Chromate-Dichromate and used those results to test the reactions when temperature was
increased and decreased. Based off these color changing results the chemical system shift was
able to be determined.
Materials and Methods:
The materials used to perform these exercises were the usual safety items (gloves & goggles),
24-well plate, coffee cup, ice cubes, tap water, 10mL of 2M Hydrochloric acid (HCl), 2mL of
0.1M Iron (III) Nitrate, 2mL of 1M Potassium Chromate, 2mL of 0.2M Potassium Ferrocyanide,
10mL of 2M Sodium hydroxide and short stem pipets. First the chemical equilibrium was
determined by adding HCl to the potassium chromate to form dichromate. Once this was
achieved the color change results were recorded. To that mixture sodium hydroxide was added to
test the change back toward reactants and this color change was recorded. Next HCl and
potassium chromate were combined, and the mixture was placed in a short stem pipet to test
under decreased temperature (ice water) and increased temperature (hot water). Under these
conditions the color of the mixture changed, and the results were recorded. The chemical
equilibrium of ferric ferrocyanide was than tested by adding sodium hydroxide to a mixture of
potassium ferrocyanide and Iron (III) nitrate, the color changing results were than recorded.
From those results determinations of chemical shifts can be made.