The electrolyte concentration in a nickel-cadmium battery is highest when the battery is ______.

The electrolyte concentration in a nickel-cadmium battery is highest when the battery is ______.

• A. Fully charged
• B. Discharged
• C. Resting
• D. Overcharged

Answer: (A)

The key idea is that the electrolyte concentration in an alkaline NiCd cell changes with state of charge because charging drives electrolysis of water at the electrodes. As charging proceeds toward full, water is split into hydrogen and oxygen and the gases escape, removing water from the liquid. With less water in the same amount of dissolved ions, the solution becomes more concentrated. Therefore, the electrolyte ends up with the highest concentration when the battery is fully charged. When the cell is discharged, the opposite trend occurs and the liquid is more dilute, and resting states show little change.

The key idea is that the electrolyte concentration in an alkaline NiCd cell changes with state of charge because charging drives electrolysis of water at the electrodes. As charging proceeds toward full, water is split into hydrogen and oxygen and the gases escape, removing water from the liquid. With less water in the same amount of dissolved ions, the solution becomes more concentrated. Therefore, the electrolyte ends up with the highest concentration when the battery is fully charged. When the cell is discharged, the opposite trend occurs and the liquid is more dilute, and resting states show little change.