# Is anode actually ever negative?

Disclaimer: This question comes from a physics student.

I was studying electrostatics and I was wondering how to charge a conductor at home without any fancy furs etc. So an idea came to me: take a battery, touch for example the negative terminal with the conductor and then remove it. Since the negative battery terminal is at a negative potential and the conductor was previously grounded ($$V = 0$$) then as their potentials must become equal, it means that electrons will flow from the battery terminal to the conductor for a short period of time. Afterwards, I disconnect the conductor and the electrons remain 'trapped' in it hence the conductor is now negatively charged.

At least that was the idea. Now suppose that the battery is a galvanic cell ($$Zn, Cu$$). The question is whether there are free electrons floating inside the $$Zn$$ anode when it is not connected to the cathode?

The whole system (battery, wires) is electroneutral while the current is flowing e.g. Zinc atoms at anode dissolve and electrons stay at the anode while the $$Zn^{2+}$$ ions go to the solution, but in the same instant other electrons leave the anode.

When the electrodes are not connected, I'm not sure would the redox reactions happen. In my understanding, $$Zn$$ oxidizes because $$Cu$$ on the other side has greater electron affinity, but $$Zn$$ would have to be able to 'sense' $$Cu$$ on the other side somehow, otherwise the oxidation reaction happens anyways for a short time until it reaches some equilibrium point. This is what I think actually happens and that's why the anode would actually be negative until connected to the cathode.

So am I on the right track with this and ultimately, will my attempt to charge the conductor a bit succeed?

• Jan 17, 2020 at 16:07
• If the anode is ever negative depends in the first place on the large scale electrostatic gradient between the ionosphere and the Earth, than on mesoscale deviation around thunderstorms and than on local electrostatic conditions. Electrode potential is conventionally related to standard hydrogen electrode, that has itself potential cca +4.4 V wrt free electron. But the potential of the free electron depends on environment potential, what brings us to the beginning. Jan 18, 2020 at 11:18
• @Poutnik That was another question that was bothering me, thank you for mentioning it. I always wondered what could be the voltage relationship between the battery terminals and a piece of electroneutral conductor and could I always or ever take it to be $0V$. But now you've cleared it up to me a lot. Also, this shouldn't be a problem in attempt to charge the conductor because even though there could be no voltage between a conductor and one battery electrode because of outside conditions, we still would have the other electrode to make the charging process possible. Jan 18, 2020 at 11:37
• See the comments underneath the post as well May 11 at 3:21

It is a very good questions from a student who seems to be thinking deeply. I have been thinking to write on this topic for the last 7-8 years. In short the poles of the batteries are electrostatically charged and one can actually "sense" this charge with the help of sensitive electroscopes which were known in the time of Volta.

The label anode or cathode is not defined with respect to the electrostatic sign as explained in the post by Maurice.

Think of a large parallel capacitor. Connect one terminal of the plate to one positive terminal and the other one the negative terminal. The capacitor plates would show a electrostatic charge.

By all means, using one single cell you would not be able to detect the electrostatic charge, like a charged comb. Only specialized electroscopes can sense that.

• So, just to clarify, my attempt at charging a piece of conductor by touching an electrode would succeed? Jan 18, 2020 at 1:10
• @lojle Yes you will, see my edited answer above. Jan 18, 2020 at 4:05
• Thank you for the clarification and I guess you were referring to ballistic galvanometers in the last paragraph. Now when I'm sure that a small current would rush into the conductor, I could in theory connect the conductor to a terminal via a ballistic galvanometer and observe a deflection on the galvanometer. Now the amount it deflects is a matter of conductor capacitance, battery voltage and the galvanometer sensitivity. Jan 18, 2020 at 4:49
• @lojle, no galvanometers can only detect current. Those specialized electroscopes were called quadrant electroscopes or gold-leaf electroscopes connected to capacitors, a device well known in Volta's time. Jan 18, 2020 at 4:52
• I think that the idea is that there would be a brief, small current not a steady one. E.g. if you connect a capacitor to a battery you will get a transient current. Whether it would be measurable in the OP's case without sophisticated equipment is a harder question. Jan 18, 2020 at 10:14

An anode is the place where oxidation occurs. In a galvanic cell, like the Daniell cell ($$Zn - Cu$$), the $$Zn$$ is oxidized at the Minus pole. $$Zn$$ is oxidized into $$Zn^{2+}$$ ion and the electrons are sent in the electric connexion going to the $$Cu$$ electrode. $$Zn$$ is the anode (negative sign) and $$Cu$$ is the cathode (positive sign)

If the same setup is used in electrolysis, the phenomena a going in the reverse sense. Electrons are obliged to flow from the copper plate to the zinc plate. $$Zn^{2+}$$ ions are reduced to metallic $$Zn$$ on the $$Zn$$ plate. The zinc plate is now working in the anode mode. But it is still the Minus pole, as, in electrolysis, cations (positive ions) are attracted by the negative pole. In the electrolysis, the $$Cu$$ plate is oxidized into $$Cu^{2+}$$ ions : Copper is the anode.

When comparing the same chemical equation working in a galvanic cell or in an electrolysis, $$Zn$$ is always the negative pole and $$Cu$$ is always the positive pole. The signs PLUS (+) or MINUS (-) can be printed on the plates. But Zn is an anode in a galvanic cell, and becomes cathode in an electrolysis system.

So you see that an anode is not always negative. The anode is the negative pole (Zn) in a galvanic cell. The anode is the positive pole (Cu) in electrolysis.

• That is a good point. But my question wasn't Is the anode always negative, but rather Is the anode ever negative? Namely, is the anode metal plate negatively charged even without considering the cathode. Maybe the question could be reduced to Does $Zn$ oxidize in $ZnSO_4$ solution at least a bit without cathode existing at all? But since in the battery we also have the salt brigde, I am not sure whether this simplification is possible... Jan 18, 2020 at 1:07
• Zinc placed in water will oxidize reducing the water to H2, the metal acts as both anode and cathode. [adding acid will accelerate everything] The chemistry is determined by the electrode potentials and the physical layout. The question you seem to be asking is were I to place a pure zinc rod in a large amount of water would zinc ions migrate from the rod leaving the electrons on the zinc. That is what seems to happen but as the charge builds up those electrons don't sit there idlily. May 13 at 3:48