The conductimetric method for ammonia detection relies on which observable change?

• A. Increase in conductivity due to ammonium and CO2
• B. Color change to yellow
• C. Decrease in conductivity
• D. No change

Answer: (A)

The main idea is that conductivity sensing relies on how many free ions are in the solution. When ammonia is detected with a conductimetric method, the reactions in the sensor produce ionic species—such as ammonium and carbonate/bicarbonate ions from dissolved CO2. More ions mean the solution conducts electricity better, so the measured conductivity increases. That rise in conductance is the observable signal for ammonia.

Color change wouldn’t be seen in this method, since it relies on electrical, not optical, changes. A decrease in conductivity would imply fewer ions, which isn’t what occurs here, and no change would ignore the ion production that accompanies the reaction.