The following acidic galvanic cell is set-up with the following overall cell reaction +7 H2O1) 14 H* (aq) + Cr207 (aq) + 6 Age) → 6 Ag*(aq) + 2 Cr**c@q) V Porous Barrier Pt Ag 0.22 M Na2Cr207 0.25 M Cr(NO3)3 0.20 M AGNO3 If the cell voltage is 0.257 V, what is the pH of the cell?

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ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
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### Standard Reduction Potentials

The table below provides standard reduction potentials (E°) for various redox couples. The standard reduction potential is an important concept in electrochemistry, indicating the tendency of a chemical species to gain electrons and thereby be reduced. The more positive the reduction potential, the greater the species' affinity for electrons, and thus its tendency to be reduced is higher.

#### Table: Standard Reduction Potentials

| **Couple**       |                   | **E° (Volts)** | **Couple**      |                 | **E° (Volts)**  |
|------------------|-------------------|-------------|----------------|---------------|-------------|
| F₂               | ---- HF (H⁺)         | +3.03       | SO₄²⁻           | ---- H₂SO₃ (H⁺) | +0.20       |
| F₂               | ---- F⁻               | +2.87       | Sn⁴⁺            | ---- Sn²⁺          | +0.15       |
| S₂O₈²⁻         | ---- SO₄²⁻          | +2.05       | S                     | ---- H₂S (H⁺)      | +0.141     |
| BiO₃⁻         | ---- Bi³⁺              | +2.0         | Hg₂Br₂        | ---- Hg (Br⁻)   | +0.140     |
| H₂O₂           | ---- H₂O (H⁺)      | +1.78       | AgBr           | ---- Ag (Br⁻)    | +0.0713   |
| PbO₂           | PbSO₄ (H⁺, SO₄²⁻) | +1.685    | H⁺                  | ---- H₂               | +0.0000   |
| Ce⁴⁺            | ---- Ce³⁺            | +1.61       | Pb²⁺            | ---- Pb               | -0.126      |
| MnO₄⁻        | ---- Mn²⁺ (H⁺)      | +1.491    | Sn²⁺             | ---- Sn              | -0.136      |
| ClO₃⁻          | ---- Cl⁻               | +1.47       | AgI
Transcribed Image Text:--- ### Standard Reduction Potentials The table below provides standard reduction potentials (E°) for various redox couples. The standard reduction potential is an important concept in electrochemistry, indicating the tendency of a chemical species to gain electrons and thereby be reduced. The more positive the reduction potential, the greater the species' affinity for electrons, and thus its tendency to be reduced is higher. #### Table: Standard Reduction Potentials | **Couple** | | **E° (Volts)** | **Couple** | | **E° (Volts)** | |------------------|-------------------|-------------|----------------|---------------|-------------| | F₂ | ---- HF (H⁺) | +3.03 | SO₄²⁻ | ---- H₂SO₃ (H⁺) | +0.20 | | F₂ | ---- F⁻ | +2.87 | Sn⁴⁺ | ---- Sn²⁺ | +0.15 | | S₂O₈²⁻ | ---- SO₄²⁻ | +2.05 | S | ---- H₂S (H⁺) | +0.141 | | BiO₃⁻ | ---- Bi³⁺ | +2.0 | Hg₂Br₂ | ---- Hg (Br⁻) | +0.140 | | H₂O₂ | ---- H₂O (H⁺) | +1.78 | AgBr | ---- Ag (Br⁻) | +0.0713 | | PbO₂ | PbSO₄ (H⁺, SO₄²⁻) | +1.685 | H⁺ | ---- H₂ | +0.0000 | | Ce⁴⁺ | ---- Ce³⁺ | +1.61 | Pb²⁺ | ---- Pb | -0.126 | | MnO₄⁻ | ---- Mn²⁺ (H⁺) | +1.491 | Sn²⁺ | ---- Sn | -0.136 | | ClO₃⁻ | ---- Cl⁻ | +1.47 | AgI
### Acidic Galvanic Cell Setup and pH Determination

#### The Cell Reaction
The acidic galvanic cell is set up with the following overall cell reaction:

\[14 \text{H}^+_{\text{(aq)}} + \text{Cr}_2\text{O}_7^{2-} _{\text{(aq)}}+ 6 \text{Ag}_{\text{(s)}} \rightarrow 6 \text{Ag}^+_{\text{(aq)}} + 2 \text{Cr}^{3+}_{\text{(aq)}} + 7 \text{H}_2\text{O}_{\text{(l)}}\]

#### Diagram Description
The diagram represents a galvanic cell with:

- A porous barrier separating the two half-cells.
- The left half-cell contains a Platinum (Pt) electrode immersed in a solution of 0.22 M Na\(_2\)Cr\(_2\)O\(_7\) and 0.25 M Cr(NO\(_3\))\(_3\).
- The right half-cell contains a Silver (Ag) electrode immersed in a 0.20 M AgNO\(_3\) solution.
- The setup includes a voltmeter (V) connected between the two electrodes, indicating the cell voltage.

#### Problem Statement
"If the cell voltage is 0.257 V, what is the pH of the cell?"

To solve this, you would use the Nernst equation and other relevant electrochemical principles to find the pH of the solution in the galvanic cell based on the given conditions.
Transcribed Image Text:### Acidic Galvanic Cell Setup and pH Determination #### The Cell Reaction The acidic galvanic cell is set up with the following overall cell reaction: \[14 \text{H}^+_{\text{(aq)}} + \text{Cr}_2\text{O}_7^{2-} _{\text{(aq)}}+ 6 \text{Ag}_{\text{(s)}} \rightarrow 6 \text{Ag}^+_{\text{(aq)}} + 2 \text{Cr}^{3+}_{\text{(aq)}} + 7 \text{H}_2\text{O}_{\text{(l)}}\] #### Diagram Description The diagram represents a galvanic cell with: - A porous barrier separating the two half-cells. - The left half-cell contains a Platinum (Pt) electrode immersed in a solution of 0.22 M Na\(_2\)Cr\(_2\)O\(_7\) and 0.25 M Cr(NO\(_3\))\(_3\). - The right half-cell contains a Silver (Ag) electrode immersed in a 0.20 M AgNO\(_3\) solution. - The setup includes a voltmeter (V) connected between the two electrodes, indicating the cell voltage. #### Problem Statement "If the cell voltage is 0.257 V, what is the pH of the cell?" To solve this, you would use the Nernst equation and other relevant electrochemical principles to find the pH of the solution in the galvanic cell based on the given conditions.
Expert Solution
Introduction:

The potential across any specified cell is computed using all species' concentration and its standard potential. This expression is also recognized as "Nernst equation" and it also contains the term denoting electrons transferred.

Given:

The temperature is 25 degree Celsius.

The concentration of silver ions is 0.20 M.

The concentration of chromium ions is 0.25 M.

The concentration of chromate ions is 0.22 M.

The cell voltage is 0.257 V.

Solution:

The given reaction is as follows:

Chemistry homework question answer, step 2, image 1

 

The oxidation half-reaction at anode is shown below.

Chemistry homework question answer, step 2, image 2

 

The reduction half-reaction at cathode is shown below.

Chemistry homework question answer, step 2, image 3

 

Multiply oxidation-half with 6 and then add oxidation and reduction half-reactions to obtain net reaction as shown below.

Chemistry homework question answer, step 2, image 4

 

The formula to calculate pH is as follows:

Chemistry homework question answer, step 2, image 5

 

The concentration of hydronium ions is calculated Nernst equation as shown below.

Chemistry homework question answer, step 2, image 6

Here,

The number of electrons transfer in the reaction is “n”.

The cell potential is “Ecell”.

The standard cell potential is “”.

 

It clear from the half-reactions that the number of electrons transferred is 6 (n=6).

The formula to calculate standard cell potential is shown below.

Chemistry homework question answer, step 2, image 7

Here,

The electrode potential of cathode is +1.33 V.

The electrode potential of anode is +0.7996 V.

 

Substitute the values in equation (III).

Chemistry homework question answer, step 2, image 8

 

Suppose the concentration of hydrogen ions is x.

Substitute all known values in equation (II).

Chemistry homework question answer, step 2, image 9

 

On further solving the equation,

Chemistry homework question answer, step 2, image 10

 

Solving the equation for the value of x:

Chemistry homework question answer, step 2, image 11

Substitute the concentration of hydrogen ions in equation (I).

Chemistry homework question answer, step 2, image 12

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