When a few drops of phenol red indicator (HPr(aq)/ Pr^-(aq)) are added to a 100.0 mL sample of 0.50 mol/L nitrous acid (HNO2(aq)), the indicator will undergo a color change.
Phenol red is an acid-base indicator that changes color depending on the pH of the solution. In an acidic solution, it appears yellow, while in a basic solution, it appears red. Nitrous acid is a weak acid, so it will partially dissociate in water to produce hydronium ions (H3O+) and nitrite ions (NO2-).
The nitrous acid will react with water according to the following equilibrium:
HNO2(aq) + H2O(l) ⇌ H3O+(aq) + NO2-(aq)
Since nitrous acid is a weak acid, it will not completely dissociate, and only a fraction of it will produce hydronium ions. As a result, the pH of the nitrous acid solution will be less than 7.
When phenol red is added, it will change its color to yellow, indicating the acidic nature of the solution. This is because the phenol red indicator is more yellow in an acidic environment.
Therefore, when a few drops of phenol red indicator are added to a 100.0 mL sample of 0.50 mol/L nitrous acid, the solution will turn yellow.
What would occur when a few drops of phenol red indicator HPr(aq)/ Pr^-(aq) are added to a 100.0mL sample of 0.50mol/L nitrous acid?
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1 answer