MCAT electrochemistry concentration cells

What is a concentration cell?

A concentration cell is an electrochemical cell where both electrodes are made of the same material but differ in ion concentration.

True or False: Concentration cells generate voltage without differing electrode materials.

True - Voltage arises from concentration differences, not different materials.

Identify the components of a concentration cell.

- Two electrodes - Electrolyte solutions - Salt bridge or porous barrier

How does ion concentration affect cell potential?

Higher concentration increases the potential difference between electrodes, driving electron flow.

Fill in the blank: In a concentration cell, the anode has __________ concentration.

lower

Write the Nernst equation.

$\displaystyle E = E^\circ - \\frac{RT}{nF} \ln Q$

What happens at the cathode of a concentration cell?

Reduction occurs as electrons flow to the electrode with higher ion concentration.

Difference between a concentration cell and a galvanic cell.

Concentration cells use identical electrodes; galvanic cells use different materials.

Cause → Effect: Increased concentration difference causes __________.

increased voltage output

Example: Calculate cell potential for a concentration cell.

Given: $\displaystyle [A^+] = 0.1 M$, $\displaystyle [B^+] = 1.0 M$. $\displaystyle E = E^\circ - \\frac{RT}{F} \ln \\frac{0.1}{1.0}$

What is the role of the salt bridge?

The salt bridge maintains charge balance by allowing ion flow, completing the circuit.

True or False: Concentration cells can only operate at standard conditions.

False - Concentration cells operate under non-standard conditions based on concentration differences.

What does the Nernst equation calculate?

The Nernst equation calculates the cell potential (E) of an electrochemical cell under non-standard conditions.

Nernst equation formula?

$\displaystyle E = E^{ heta} - \\frac{RT}{nF} \ln Q$ where: - $\displaystyle E^{ heta}$: standard potential - $\displaystyle R$: gas constant - $\displaystyle T$: temperature (K) - $\displaystyle n$: moles of electrons - $\displaystyle F$: Faraday's constant - $\displaystyle Q$: reaction quotient.

True or False: Nernst equation applies to standard conditions only.

False. The Nernst equation applies to any concentration, not just standard conditions.

Concentration cell voltage behavior?

Voltage increases as concentration difference increases; it approaches zero as concentrations equalize.

Fill in the blank: At 298 K, the Nernst equation simplifies to: $\displaystyle E = E^{ heta} - 0.0592/n \log Q$.

This simplification occurs under standard temperature.

Calculate E for a cell with concentrations 0.01 M and 1 M.

Using $\displaystyle E = E^{ heta} - 0.0592/n \log \left( \\frac{[A]}{[B]} \right)$, replace $\displaystyle [A]$ and $\displaystyle [B]$.

Concentration ratio in Nernst equation?

$\displaystyle Q = \\frac{[oxidized]}{[reduced]}$. It is crucial for cell potential calculations.

Effect of temperature on Nernst equation?

Increasing temperature increases kinetic energy, affecting $\displaystyle E$ due to changes in $\displaystyle RT$ term.

Nernst equation application in biological systems?

Used to calculate membrane potentials, like in neurons and muscle cells.

Compare standard and non-standard cell potentials.

Standard: measured at 1 M, 1 atm, 25°C. Non-standard: varies with concentration.

What is the significance of $\displaystyle E^{ heta}$ in the Nernst equation?

$\displaystyle E^{ heta}$ indicates the maximum potential under standard conditions, guiding equilibrium predictions.

Question: How does concentration affect cell potential?

Higher concentration of reactants increases cell potential, according to the Nernst equation.

What is electrode potential?

The measure of the tendency of an electrode to gain or lose electrons; expressed in volts (V).

How does concentration affect cell potential?

Increased concentration of reactants raises the cell potential; decreased concentration lowers it.

True or False: Higher ion concentration always leads to higher cell potential.

False; potential depends on both concentrations and the specific half-reactions involved.

Fill in the blank: In a concentration cell, the electrode with higher concentration acts as the _____.

anode.

How is cell potential calculated in concentration cells?

Using the Nernst equation: $\displaystyle E = E^{\circ} - \\frac{RT}{nF} \ln Q$.

Anode vs. Cathode in concentration cells?

- Anode: Lower concentration - Cathode: Higher concentration

Effect of dilution on cell behavior?

Diluting the solution decreases the concentration, which reduces cell potential; reaction may reverse.

Example: Calculate potential difference.

If $\displaystyle E^{\circ} = 0.77V$, $\displaystyle [A] = 0.1M$, $\displaystyle [B] = 1M$: $\displaystyle E = 0.77 - \\frac{0.0592}{n} \log(10)$.

What happens when concentrations equalize?

Cell potential drops to zero; the reaction reaches equilibrium and stops.

Greater concentration difference leads to?

Higher cell potential; drives the reaction forward more strongly.

Cause → Effect: Increasing reactant concentration leads to?

Increased driving force for the redox reaction.

Difference between standard cell potential and actual cell potential?

Standard potential ($\displaystyle E^{\circ}$) is measured under standard conditions; actual potential ($\displaystyle E$) is under specific conditions.