Le Chatelier Lab

LeChatelier Lab

Equilibrium #1

CH3COO- + H+  CH3COOH

When HCl was added to sodium acetate, H+ ions were added. Since the H+ ion concentration increased, this shifted the reaction to the right resulting in the production of CH3COOH- and a vinegar smell.

When NaOH was subsequently added, OH- ions were added to the solution. The OH- ions combined with the H+ ions, thereby reducing the concentration of H+. This shifted the reaction to the left, eliminating the smell.

Equilibrium #2

H2Tb  H+ + HTb-

Bromothymol blue is a pH indicator.

When HCl was added to bromothymol blue in water, H+ ions were added. Since the H+ ion concentration increased, this shifted the reaction to the left resulting in a colour change from blue to orange.

When NaOH was subsequently added, OH- ions were added to the solution. The OH- ions combined with the H+ ions, thereby reducing the concentration of H+. This shifted the reaction to the right and returning the colour from orange to blue.

Equilibrium #3

NH4+  NH3 + H+

When NaOH was added, OH- ions were added to the solution. The OH- ions combined with the H+ ions, thereby reducing the concentration of H+. This shifted the reaction to the right and producing a windex smell.

When HCl was added to sodium acetate, H+ ions were added. Since the H+ ions combined with the OH- ions, the concentration of H+ increased. This shifted the reaction to the left, eliminating the smell.

Equilibrium #4

Fe3+ + SCN-  FeSCN2+

(1) When Fe(NO3)3-9H2O crystals were added, the [Fe3+] increased. To counteract this change, the equilibrium shifted towards the products (right), which caused the solution to turn a red wine colour.

(2) When KSCN crystals were added, the [SCN-] increased. To counteract this change, the equilibrium shifted towards the products (right), which caused the solution to turn a red wine colour.

(3) When NaHPO4 crystals were added, the HPO4 2- ions reacted with the Fe3+ ions, decreasing [Fe3+]. To counteract this change, the equilibrium shifted towards the reactants (left), which caused the solution to turn colourless.

(4) When Fe(NO3)3- 9H2O was added to this solution, the [Fe3+] was increased. In order to counteract this change, the reaction shifted back right towards the products returning the colour to red.

(5) When the temperature was increased, the solution changed from deep red to colourless, with orange precipitate. This demonstrated a shift towards the reactants (left). Therefore, if heat was added to shift the reaction left,

...