Electrochemistry Lecture – Practice Flashcards

These flashcards review key concepts from the Electrochemistry lecture, including redox fundamentals, Galvanic cells, cell potentials, pH and ion-selective electrodes, calibration, maintenance, and practical biomedical applications.

What is oxidation in terms of electrons?

The loss of electrons.

What is reduction in terms of electrons?

The gain of electrons.

Which mnemonic summarizes oxidation and reduction?

OIL RIG

During a redox reaction, what is transferred between reactants?

Electrons.

Define an oxidizing agent.

A substance that accepts electrons and is reduced.

Define a reducing agent.

A substance that donates electrons and is oxidized.

In the reaction 2 Mg + O₂ → 2 Mg²⁺ + 2 O²⁻, which species is the oxidizing agent?

O₂ (oxygen).

In the same Mg/O₂ reaction, which species is the reducing agent?

Mg (magnesium).

How do direct and indirect redox reactions differ?

Direct reactions mix oxidant and reductant; indirect reactions keep them separate but electrically connected.

Which electrochemical cell type uses an indirect redox reaction to generate electricity?

A Galvanic (voltaic) cell.

What is the purpose of a salt bridge in a Galvanic cell?

To maintain electrical neutrality by allowing ion flow between half-cells.

Which electrode donates electrons in a Galvanic cell?

The anode.

Which electrode accepts electrons in a Galvanic cell?

The cathode.

In what direction do electrons flow inside an external circuit of a Galvanic cell?

From the anode to the cathode.

How is standard cell notation written?

Anode phases | salt bridge | cathode phases, with single vertical lines separating phases.

Name three factors that influence the measured cell potential (Ecell).

The specific half-reactions, ion concentrations, and temperature.

Define electromotive force (Ecell).

The difference between the cathode potential and the anode potential.

What electrode is universally used as the reference for standard potentials?

The Standard Hydrogen Electrode (SHE).

What potential (E°) is assigned to the SHE?

0 V.

How do you know which substance is more easily reduced from a table of E° values?

The one with the more positive standard reduction potential.

What happens to E° when a half-reaction is reversed?

Its sign is reversed.

Does scaling a half-reaction (changing coefficients) change its E°?

No; E° is independent of stoichiometric coefficients.

What criterion predicts spontaneity of a redox reaction?

Ecell greater than 0 indicates a spontaneous reaction.

In a standard Ag⁺/Ag vs Cu²⁺/Cu cell, which electrode becomes the cathode?

The silver electrode (Ag⁺ is reduced).

What is the standard Ecell for the spontaneous Ag/Cu system?

+0.46 V.

What device converts spontaneous chemical energy into electrical energy?

A battery (voltaic cell).

Give an everyday example of a Galvanic cell in corrosion.

Rusting of iron in water.

Define potentiometry.

Direct measurement of electrical potential caused by the activity of free ions.

Which two electrodes are required in any potentiometric system?

A measuring electrode and a reference electrode.

Name two common reference electrodes.

Silver/Silver Chloride (Ag/AgCl) and Calomel (Hg/Hg₂Cl₂).

List the main components of a glass pH electrode.

Special pH-sensitive glass membrane, internal HCl solution, internal Ag/AgCl reference, external reference junction.

Why is the hydrated gel layer on a glass electrode crucial?

It allows selective exchange of H⁺ ions, enabling pH measurement.

Which equation relates electrode potential to ion activity?

The Nernst Equation.

Which variable in the Nernst equation requires temperature compensation?

Temperature (T).

How many buffer solutions are needed to calibrate a pH meter?

At least two buffers.

How should calibration buffers be chosen?

They must bracket the expected sample pH range.

What is the preferred storage medium for the glass bulb of a pH electrode?

Pure (distilled) water.

Why avoid immersing the reference junction of a combination electrode in KCl during storage?

Silver chloride can precipitate and block the junction.

What common hardware problem causes many electrode errors?

A blocked or contaminated reference junction.

After rinsing an electrode, what should you avoid doing?

Wiping or rubbing the membrane; let it drip dry.

What basic principle do ion selective electrodes (ISEs) rely on?

Measuring the potential across a selective membrane proportional to target ion activity.

Which ionophore gives potassium electrodes their selectivity?

Valinomycin.

Approximately how much more selective is a sodium ISE for Na⁺ over K⁺?

About 300 : 1.

What type of membrane does a sodium ISE employ?

A sodium-selective glass membrane.

What does a calcium ISE measure in plasma?

Free (ionized) calcium concentration.

Give three advantages of ion selective electrodes.

No reagents/standard curve needed, rapid and cost-effective analysis, high selectivity and sensitivity.

Why should the sample be agitated during ISE measurements?

To maintain constant ion flow to the sensor for stable readings.

If sample concentrations are unknown, how many standards should you use for ISE calibration?

At least three spanning the expected range.

How should an ISE be stored when not in use?

Keep the membrane moist in a beaker of water.

How does a CO₂ gas electrode function?

CO₂ forms carbonic acid, lowering pH, which is detected by a modified pH electrode.

What critical maintenance step extends reference electrode life?

Regularly renewing the internal filling solution.

What does a pH electrode actually measure: concentration or activity of H⁺?

It measures hydrogen ion activity.

Why is the pH meter first set to pH 7 during calibration?

To establish the zero point before adjusting the slope.

If a pH meter lacks a slope control, which feature compensates for slope changes?

The temperature compensator control.

How does temperature affect pH readings?

It changes electrode potential via the Nernst equation, so compensation is required.