As 1 g of sodium hydroxide dissolves in 100 g of water, the conductivity of the water:

• A. Remains the same
• B. Cannot be determined from given information
• C. Decreases
• D. Increases

Answer: (D)

Conductivity of a solution rises with the number of charge carriers. Sodium hydroxide is a strong electrolyte, so it dissociates almost completely in water into Na+ and OH− ions. Each unit of NaOH therefore creates two mobile ions that can carry current. Adding 1 g of NaOH to 100 g of water introduces more ions than are present in pure water, so the solution conducts electricity better. Since pure water has relatively few ions, the overall effect is an increase in conductivity.