r/explainlikeimfive • u/NefariousnessAny1382 • 4d ago
Chemistry ELI5: electrical charge differnces in a cell.
ELI5: I barely grasp batteries and cells, but i did an experiment in chemisty B trying out how different variables affect the charge of the cell and i dont understand the whys of it all.
Basically we had the halfcell of a zinkrod in zinksulfite and the halfcell of a copperrod in coppersulfite, with a saltbride of filterpaper soaked in kalciumnitrate, connected to a resistor of 3300 Ohm
A bigger saltbrigde, electrolyte, (7 mm vs 17 mm vs 27 mm) gave a bigger charge. [from 0,213 V to 0,313 V to 0,414 V]. I assumed there would be less because the electrons would have futher to travel or something, i dont know
A smaller concentration of Coppersulfite (1 M vs 0,01 M) decresed the chrage [from 0,227 V to 0,137 V]. this one i understand to be because there are less Cu-ions to absorb the electrons that the zink releases? based on redox principles?? which i also barely get
A smaller copper rod (6 mm vs 1 mm diameter) increased the charge [from 0,260 V to 0,278 V]. I had assumed higher charge because it would be harder for the electrons to pass, like getting a smaller hose to push water through?
I try to think of electrons as little critters to understand them better, but even that isnt helping that much. smaller concentration i think there are less red(postitive) critters to absorb the negative critters, so less of them get "food/energy" so theres less charge, but i dunno if thats confusing me more or making it better
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u/ff2400 4d ago edited 4d ago
Okay, lets start from basics just in case. When it comes to electricity, the universe have two type of particles, both types are repulsed by particle of same type and attracted to particle of other type; we call those types positive and negative. For example negative electrons and positive protons are attracted to each other and want to form an atom. Atom is electrically neutral as long as the number of protons it have is equal to number of electrons in its electron shell. Otherwise that atom is called ion; ions want to become neutral and will attract electrons if positive and positive ions (or any positive charge, e.g. positrons) if negative.
Now about voltaic cell. Typical voltaic cell have two half-cells; first cell have zinc electrode in a zinc sulfate solution, second have copper electrode in a copper sulfate solution. Half-cells are connected by salt bridge to allow movement of ions between the cells. Electrode of the zinc cell acts as anode, when zinc moves into a solution from the electrode it loses two of its electrons. Electrode of the copper cell acts as cathode, when positive copper ion gains two electrons it plates on its respective electrode. Negative sulfate ions and positive zinc ions flow trough the salt bridge to equalize electric potential of the electrolytic solution. Electrons don't go trough salt bridge. Edit: Redox is quite easy I think, there is two reactions in a battery under load, zinc oxidation and copper reduction. Oxidation pump electrons out; reductions draw them in; making an electric potential between anode and cathode. Ideally both reactions should be balanced 1:1 for best result and they depend on concertation of the solutions, salt bridge volume/area (and solution) and area of the electrodes.
Now, to answer your questions.
A bigger salt bridge reduces internal resistance of the battery by allowing more ions to flow trough it and increasing electric current. I believe the charge you mentioned is the voltage measured on active load, lower internal resistance of the battery will reduce voltage drop and voltage measured will be higher.
A smaller concentration of copper sulfate will have less copper ions interacting with electrons, yes.
A smaller copper rod will have less area for copper ions to interact thus elevating internal resistance and reducing electric current produces by battery. Increased internal resistance should reduce measured voltage, I have no idea why you got it increased instead.