Question

A pH meter employs a voltaic cell for which the cell potential is very sensitive to...

A pH meter employs a voltaic cell for which the cell potential is very sensitive to pH. A simple (but impractical) pH meter can be constructed by using two hydrogen electrodes: one standard hydrogen electrode and a hydrogen electrode (with 1 atm pressure of H2 gas) dipped into the solution of unknown pH. The two half-cells are connected by a salt bridge or porous glass disk.

a)Write the half-cell reactions for the cell.

1) No reaction.

2) H+(aq,1M)+H2O(l)→H3O+(aq), H2(g)→2H+(aq,1M)+2e−.

3) 2H2O(l)+2e−→2OH−(aq)+H2(g), H2(g)→2H+(aq,1M)+2e−.

4) 2H+(aq,1M)+2e−→H2(g), H2(g)→2H+(aq,1M)+2e−.

b) Calculate the standard Ecell.

c)What is the pH of the solution in the half-cell that has the standard hydrogen electrode?

d)What is the Ecell when the pH of the unknown solution is 6.0?

Homework Answers

Answer #1

a. This is a concentration cell.

In the lower H+ concentration   half cell   the reaction is    H2(g)→2H+(aq,1M)+2e−.

In the higher H+ concentration   half cell   the reaction is 2H+(aq,1M)+2e−→H2(g)

Answer a.4.    In fact the measurement is made with a high impedance voltmeter (the current is very close to 0), thus the measurement is not modifying in a significant way, the cell concentrations.

b. In a concentration cell, Eo is always =0.

c. [H+] = 1 M in standard condition, thus pH = 0

d. E = - 0.0592 V · log (1M/1x10-6M) =

          - 0.0592 V · 6 = -0.3552 V vs NHE

Know the answer?
Your Answer:

Post as a guest

Your Name:

What's your source?

Earn Coins

Coins can be redeemed for fabulous gifts.

Not the answer you're looking for?
Ask your own homework help question
Similar Questions
A voltaic cell is constructed in which the cathode is a standard hydrogen electrode and the...
A voltaic cell is constructed in which the cathode is a standard hydrogen electrode and the anode is a hydrogen electrode (P(H2) = 1 atm) immersed in a solution of unknown [H+]. If the cell potential is 0.179 V, what is the pH of the unknown solution at 298 K?
The cell potential of the following electrochemical cell depends on the pH of the solution in...
The cell potential of the following electrochemical cell depends on the pH of the solution in the anode half-cell: Pt(s)|H2(g,1atm)|H+(aq,?M)||Cu2+(aq,1.0M)|Cu(s). What is the pH of the solution if Ecell is 360 mV ?
Given the measured cell potential, Ecell, is -0.3635 V at 25'C. In the following cell, calculate...
Given the measured cell potential, Ecell, is -0.3635 V at 25'C. In the following cell, calculate the H+ concentration. Pt(s)/H2(g, 0.829 atm)/H+(aq, ?M)//Cd+2(aq,1.00M)/Cd(s) The balanced reduction half-reactions for the cell, and their respective standard reduction potential values, E' are as followed. 2H+(aq)+2e- -> H2(g) E= 0.00V Cd+2(aq) +2e- ->Cd(s) E= -0.403V [H+]= ?
1)A standard galvanic cell is constructed in which a H+ | H2 half cell acts as...
1)A standard galvanic cell is constructed in which a H+ | H2 half cell acts as the cathode. Which of the following statements are correct? Hint: Refer to a table of standard reduction potentials. (Choose all that apply.) a) H2 is oxidized at the cathode. b) The cathode reaction is 2H+ + 2e- -> H2 c) Mn2+|Mn could be the other standard half cell. d) Fe3+|Fe2+ could be the other standard half cell. e) In the external circuit, electrons flow...
Use the standard reduction potentials shown here to answer the questions. Reduction half-reaction E∘ (V) Cu2+(aq)+2e−→Cu(s)...
Use the standard reduction potentials shown here to answer the questions. Reduction half-reaction E∘ (V) Cu2+(aq)+2e−→Cu(s) 0.337 2H+(aq)+2e−→H2(g) 0.000 A copper, Cu(s), electrode is immersed in a solution that is 1.00 M in ammonia, NH3, and 1.00 M in tetraamminecopper(II), [Cu(NH3)4]2+. If a standard hydrogen electrode is used as the cathode, the cell potential, Ecell, is found to be 0.073 V at 298 K. Part A Based on the cell potential, what is the concentration of Cu2+ in this solution?...
A voltaic cell is set up with copper and hydrogen half-cells. Standard conditions are employed in...
A voltaic cell is set up with copper and hydrogen half-cells. Standard conditions are employed in thecopper half-cell, Cu2+(aq, 1.00 M)|Cu(s). The hydrogen gas pressure is 1 atm, and [H+] in the hydrogen half-cell is the unknown. A value of 0.500 V is recorded for Ecellat 298 K. Determine the pH of the solution.
Exercise 20.105 Part A The cell potential of the following electrochemical cell depends on the pH...
Exercise 20.105 Part A The cell potential of the following electrochemical cell depends on the pH of the solution in the anode half-cell: Pt(s)|H2(g,1atm)|H+(aq,?M)||Cu2+(aq,1.0M)|Cu(s). What is the pH of the solution if Ecell is 370 mV ? Express your answer using two significant figures. pH = SubmitMy AnswersGive Up
A voltaic cell is constructed in which the anode is a Cr2+|Cr3+ half cell and the...
A voltaic cell is constructed in which the anode is a Cr2+|Cr3+ half cell and the cathode is a Ag|Ag+ half cell. The half-cell compartments are connected by a salt bridge. (Use the lowest possible coefficients. Use the pull-down boxes to specify states such as (aq) or (s). If a box is not needed, leave it blank.) The anode reaction is: __(aq)(s)(l)(g) + __(aq)(s)(l)(g) -----> __(aq)(s)(l)(g) + __(aq)(s)(l)(g) The cathode reaction is: __(aq)(s)(l)(g) + __ (aq)(s)(l)(g) ----->   __(aq)(s)(l)(g) + __(aq)(s)(l)(g)...
Predict the half-cell reactions that occur when aqueous solutions of the following salts are electrolyzed in...
Predict the half-cell reactions that occur when aqueous solutions of the following salts are electrolyzed in a cell with inert electrodes. What is the overall cell reaction in each case? Part A anode reaction for LiBr Express your answer as a ionic equation. Identify all of the phases in your answer. 2Br−(aq)→Br2(l)+2e− Part B cathode reaction for LiBr: Express your answer as a ionic equation. Identify all of the phases in your answer. 2H2O(l)+2e−→H2(g)+2OH−(aq) This is where I need help!...
Enter electrons as e-. A voltaic cell is constructed in which the anode is a Sn|Sn2+...
Enter electrons as e-. A voltaic cell is constructed in which the anode is a Sn|Sn2+ half cell and the cathode is a I-|I2 half cell. The half-cell compartments are connected by a salt bridge. (Use the lowest possible coefficients. Use the pull-down boxes to specify states such as (aq) or (s). If a box is not needed, leave it blank.) The anode reaction is: __(aq)(s)(l)(g) + __(aq)(s)(l)(g)   ----->   __(aq)(s)(l)(g) + __(aq)(s)(l)(g) The cathode reaction is: __(aq)(s)(l)(g) + __(aq)(s)(l)(g)   ----->...