Voltaic Cell Tuffy!!
Posted: Fri Mar 21, 2014 4:42 pm
Hi, this is my first post and will appreciate any help and comments.
I have a copper and zinc pile with the standard wet bridge. What takes place between the dissimilar metals is galvanic corrosion which is a natural and spontaneous reaction causing an electrical current or flow between the metals. Because the metals are not in direct contact and because of the wet (electrolyte) bridge if galvanic corrosion occur it must be via the electrolyte and the electrons will then flow through the electrolyte. The wet bridge is cotton soaked in an electrolyte made of a 50g NaCl per 1000ml distilled water.
Sodium Chloride breaks up in the water to make positive sodium ions (Na+) and negative chloride ions (Cl-). These ions reduce the energy needed for water to split into hydroxide ions (OH-) and hydrogen ions H+ (the hydrogen ions quickly find another water molecule and create hydronium ions, H3O+)
1. at the zinc electrode (anode)
The zinc ion combines with four hydroxide ions to form one ion of zincate (Zn(OH)42-), leaving two electrons behind on the zinc anode.
The chlorine ions from the salt then combine with the hydronium ions left over when the hydroxide ions were taken away by the zinc, and form hydrochloric acid.
Zn + 4OH => Zn(OH)42- + 2e-
4Cl + 4H20 => 4HCl + 4OH
ZN(OH)42- => ZnO + H2O + 2OH-
2. at the copper electrode (cathode)
four electrons combine with oxygen dissolved in the water and two molecules of water to form four hydroxide ions.
The sodium ions from the salt combine with these hydroxide ions to make sodium hydroxide.
The hydrochloric acid and the sodium hydroxide combine back into salt and water.
O2 + 2H2O + 4e- => 4OH
2Na+ + 4OH- => 4 NaOH
NaOH + HCl => NaCl + H2O
My questions are this:
a. Do I have the reactions correctly noted?
b. If a NaCl molecule is the end result of the reaction in the electrolyte is it acting like a sort of catalyst? because the salt comes out of the process unchanged
c. Will the copper electrode still corrode?
d. Will there be a buildup of zinc oxide on the zinc electrode?
3. We can calculate from the metallurgy Anodic Index the overall standard state cell potencial (Volts) from the half cell reactions - one being reduction (0.762 V)
and the other being oxidation (0.339 V) to yield a total of 1.101 V
My questions are:
a. Does the surface area have an effect on the voltage produced?
b. If so, what formula can be used to calculate the voltage?
c. How would I calculate the amperage of the cell? or would it be load dependant?
Then finally what can the life expectancy of such a cell be? How long will it keep producing usable electrical current?
I know I will have to put the cell in an air tight container to prevent the water in the electrolyte from evaporating and drying out!
Thank you in advance for any information that would shed some light on the questions I have. I know it is a mouthful!
Ben van der Poel
I have a copper and zinc pile with the standard wet bridge. What takes place between the dissimilar metals is galvanic corrosion which is a natural and spontaneous reaction causing an electrical current or flow between the metals. Because the metals are not in direct contact and because of the wet (electrolyte) bridge if galvanic corrosion occur it must be via the electrolyte and the electrons will then flow through the electrolyte. The wet bridge is cotton soaked in an electrolyte made of a 50g NaCl per 1000ml distilled water.
Sodium Chloride breaks up in the water to make positive sodium ions (Na+) and negative chloride ions (Cl-). These ions reduce the energy needed for water to split into hydroxide ions (OH-) and hydrogen ions H+ (the hydrogen ions quickly find another water molecule and create hydronium ions, H3O+)
1. at the zinc electrode (anode)
The zinc ion combines with four hydroxide ions to form one ion of zincate (Zn(OH)42-), leaving two electrons behind on the zinc anode.
The chlorine ions from the salt then combine with the hydronium ions left over when the hydroxide ions were taken away by the zinc, and form hydrochloric acid.
Zn + 4OH => Zn(OH)42- + 2e-
4Cl + 4H20 => 4HCl + 4OH
ZN(OH)42- => ZnO + H2O + 2OH-
2. at the copper electrode (cathode)
four electrons combine with oxygen dissolved in the water and two molecules of water to form four hydroxide ions.
The sodium ions from the salt combine with these hydroxide ions to make sodium hydroxide.
The hydrochloric acid and the sodium hydroxide combine back into salt and water.
O2 + 2H2O + 4e- => 4OH
2Na+ + 4OH- => 4 NaOH
NaOH + HCl => NaCl + H2O
My questions are this:
a. Do I have the reactions correctly noted?
b. If a NaCl molecule is the end result of the reaction in the electrolyte is it acting like a sort of catalyst? because the salt comes out of the process unchanged
c. Will the copper electrode still corrode?
d. Will there be a buildup of zinc oxide on the zinc electrode?
3. We can calculate from the metallurgy Anodic Index the overall standard state cell potencial (Volts) from the half cell reactions - one being reduction (0.762 V)
and the other being oxidation (0.339 V) to yield a total of 1.101 V
My questions are:
a. Does the surface area have an effect on the voltage produced?
b. If so, what formula can be used to calculate the voltage?
c. How would I calculate the amperage of the cell? or would it be load dependant?
Then finally what can the life expectancy of such a cell be? How long will it keep producing usable electrical current?
I know I will have to put the cell in an air tight container to prevent the water in the electrolyte from evaporating and drying out!
Thank you in advance for any information that would shed some light on the questions I have. I know it is a mouthful!
Ben van der Poel