LeChatelier's Principle Mini Lab

Joshua Whiteley & Rebecca Winkler

Solubility of Carbon Dioxide

2CO2 (g) + H2O (l) ↔ CO2 (aq) + H+ (aq) + HCO3-1 (aq)

10 mL of seltzer water and 2 mL of bromocresol green solution were added to a beaker. 10 mL of the solution was drawn up in a syringe. The initial pH of the solution was 4.2. When pressure was applied in the syringe, the color of the solution changed to a darker color, with a pH of 4.4

According to LeChaterlier, an increase in pressure causes the system to move to reduce the pressure, which means it goes in the direction that reduces the number of moles of gas. Appying more pressure to the CO2 (g) in the reaction caused the reaction to shift, and changed the acidity of the solution.

Solubility of Magnesium Hydroxide

In the original solution of just distilled water, the indicator read a pH of ~7. When adding 10 mL of a strong base, Mg(OH)2, the pH was raised to ~10 due to the presence of a base, indicated by the purple color. After adding about 20 mL of a strong acid, HCl, the reaction underwent a acid-base neutralization and then the pH dropped to approximately 4 due to the abundance of acid compared to base, causing the base to be the limiting reagent with acid leftover, indicated by a pink color. The reaction Mg(OH)2(aq) ⇌ Mg²⁺(aq) + 2OH⁻(aq) shifts to the right whenever HCl is added because the combination of H+ ions and OH- ions reduces the amount of OH- ions produced by the dissolution of Mg(OH)2, so the reaction compensates by creating more OH- ions by shifting to the right in order to try and remain in equilibrium

HCl ⇌ H⁺ + Cl⁻

Mg(OH)2(aq) ⇌ Mg²⁺(aq) + 2OH⁻(aq)

2H⁺(aq)+ Mg²⁺(aq) + 2OH-(aq) ⇌ 2H2O(l)