Is anode actually ever negative?

Question

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?

Answer 1

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.

Answer 2

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.