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In Part 1A, adding water to the cobalt (II) chloride made the solution a lighter
pink colour because it increased the concentration of water in the products of the forward
reaction, which caused the equilibrium to shift left and produce more reactants. The
addition of HCl caused a blue colour to appear since it increased the concentration of Cl-
ions, therefore causing the equilibrium to shift to the right.
In Part 1B, adding HCl to the cobalt (II) chloride solution caused the colour to
change to blue because of the aforementioned reason. Then, once water was added, the
solution changed back to pink because the addition of water increased the concentration
of water in the products. As a result, the reaction moved back to equilibrium. Lastly, the
addition of the lead (II) nitrate to the solution caused a precipitate to form, which
decreased the concentration of Cl-. Although the colour was still pink, the decrease in
concentration caused the reaction to move back to equilibrium position.
In Part 1C, adding HCl to the cobalt (II) chloride solution caused the colour to
change to blue because the addition of HCl increased the concentration of Cl- ions,
therefore causing equilibrium to shift to the right. After, once the lead (II) nitrate was
added to the solution, a precipitate formed and the equilibrium moved back, as the colour
became pink. This is due to the fact that the lead (II) nitrate decreases the concentration
of Cl-. In Part 2A, the cobalt (II) chloride was originally purple before we put it into the
ice bath. This colour is due to the fact that it is in perfect equilibrium as it is a mixture
between reactants (pink colour) and products (blue colour). Once bathing it in the ice
bath, my partner and I were able to notice that the colour changed to a light purple, which
means it was more reactant-favoured. Using equilibrium theory, this makes logical sense
because if the temperature drops, the reaction shifts in favour of the exothermic reaction.
This means that because the reverse reaction is exothermic, the forward reaction must be
In Part 2B, the cobalt (II) chloride was originally light purple before we put it into
the hot water bath. Once placed in the hot water bath, the solution slowly started to
change to a dark purple colour and this is due to the fact that an increase in temperature
causes the equilibrium position to shift in favour of the endothermic. Since the forward
reaction is endothermic, the dark purple colour makes sense.
Considering that Le Chatelier’s Principle was able to predict the colour changes
associated with the increase or decrease in temperature or concentration of the
reactants/products in the cobalt solution equilibrium, the experiment effectively shows
that Le Chatelier’s Principle is true.
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