Discussion

LeChatelier's Principle states that if a system is at equilibrium and something is changed so that it is no longer at equilibrium, the system will respond in an effort to counteract that change. If more reactant is added, the equilibrium will shift to the right in order to consume some of the extra reactant, resulting in more product. If some of the product is removed from the system, the equilibrium will shift to the right to produce more of that product. The equilibrium can be shifted to the left by either adding product to or removing reactant from the system.

Narration

Yellow chromate and orange dichromate are in equilibrium with each other in aqueous solution. The more acidic the solution, the more the equilibrium is shifted to the right towards the dichromate ion. As nitric acid is added to the chromate solution, the yellow color turns to orange. When sodium hydroxide is added to the chromate solution, the orange color turns back to yellow. The sodium hydroxide reacts with hydrogen ions, removing them from the solution. When one reactant is removed from an equilibrium system, the equilibrium shifts from the right back toward the left, in this case forming yellow chromate ion again.