A specific-ion meter resembles a _______ except for the addition of a ______ and a provision for a selective-ion electrode.

A specific-ion meter resembles a _______ except for the addition of a ______ and a provision for a selective-ion electrode.

• A. A selective-ion electrode and a millivolt scale
• B. A milliamp scale and a pH electrode
• C. A pH meter and a millivolt scale
• D. An optical detector and a voltmeter

Answer: (A)

The key idea is that measuring specific ions uses a voltage produced by an ion-selective electrode, and this setup is functionally and structurally like a pH meter. A specific-ion meter is basically a pH-meter–style instrument adapted to read voltages (millivolts) instead of pH units, and it must have a way to connect and use different ion-selective electrodes for various ions. So, it resembles a pH meter, with two additions: a millivolt-scale readout to interpret the voltage from the ion-selective electrode, and a provision to attach a selective-ion electrode so you can measure different ions. The other choices don’t fit because they don’t capture the same analogy: the device isn’t simply another selective-ion electrode itself, current (milliamp) scales aren’t what these measurements use, and an optical detector isn’t involved in this ion-specific electric-measurement approach.

The key idea is that measuring specific ions uses a voltage produced by an ion-selective electrode, and this setup is functionally and structurally like a pH meter. A specific-ion meter is basically a pH-meter–style instrument adapted to read voltages (millivolts) instead of pH units, and it must have a way to connect and use different ion-selective electrodes for various ions.

So, it resembles a pH meter, with two additions: a millivolt-scale readout to interpret the voltage from the ion-selective electrode, and a provision to attach a selective-ion electrode so you can measure different ions. The other choices don’t fit because they don’t capture the same analogy: the device isn’t simply another selective-ion electrode itself, current (milliamp) scales aren’t what these measurements use, and an optical detector isn’t involved in this ion-specific electric-measurement approach.