What is the equilibrium equation and solution color that would occur when a few drops of phenol red indicator HPr(aq) / Pr^- (aq) are added to 100 mL sample of 0.50 mol/L nitrous acid
The equilibrium equation for nitrous acid (HNO2) is:
HNO2 (aq) ⇌ H+ (aq) + NO2- (aq)
When phenol red indicator is added to the solution, it can act as an indicator for the presence of hydrogen ions (H+). Phenol red changes color depending on the pH of the solution. It is yellow in acidic solutions (pH below 6.8), red in neutral solutions (pH around 7.4), and pink in basic solutions (pH above 8.4).
In this case, the addition of phenol red indicator to the nitrous acid solution would result in the color change from its initial color to red. This is because nitrous acid is a weak acid, and its dissociation produces hydrogen ions (H+), which leads to a slightly acidic solution.
Therefore, the equilibrium equation with phenol red indicator is:
HNO2 (aq) + H2O (l) ⇌ H3O+ (aq) + NO2- (aq)
The addition of phenol red indicator would not change the equilibrium equation itself, but it would change the color of the solution to red.