Hey guys!
Sorry I have quite a long question, I was wondering whether someone could explain how a dry cell battery works or a lead-acid battery cell, I've read some textbooks about it but I'm still a bit confused! And also, what's a good way of knowing what citric acid and sodium hydroxide forms? Like what the products are.. Thank you!
Neutron
Hey Neutron!
First of all, thank you for answering amanda's question! It's really great to see everyone helping each other out! I certainly give you credit for that!
Ok, so for me, my chem teacher didnt really explain that dotpoint, so I really had to chew my jacaranda textbook and collect online informations. Im suspecting that you are perhaps thrown into the same situation too? (correct me if lm wrong haha) But dont worry, Im here to help!
If you understood galvanic cells, you should be able to reason with the chemical functionality of a dry cell battery. All it is, is just the electrode in the anode half-cell being oxidised and the electrode in the cathode half-cell being reduced, and hence producing a voltage. It works exactly like your galvanic cells, except with more complicated substances. In a dry-cell battery, the positive cathode at the centre consists of an inert graphite rod surrounded by MnO
2(s) powder. The negative anode consists of the zinc casing of the cell. And there is a thick layer of moist electrolyte paste NH
4Cl
(aq) between the graphite rod and MnO
2(s). What basically happens is essentially the reaction between manganese dioxide powder and Ammonium chloride and zinc casing and ammonium chloride . (
2MnO2(s) + 2NH4+(aq) + 2e- --> Mn2O3(s) + H2O(l) + 2NH3(aq)) In this equation, the original oxidation state of Mn is +4 but in the product, the oxidation state of Mn becomes +3.
This means that Mn has been reduced. In the zinc casing and ammonium chloride reaction (
Zn(s) + 2NH4Cl-(aq) --> ZnCl2(s) + 2NH3(aq) + H2(g)), the original oxidation state of Zinc was 0, and after the reaction, its oxidation state becomes 2+.
This means that Zinc has been oxidised. This redox reaction then produces a voltage, just like what happens in a galvanic cell.
In regards to citric acid + sodium hydroxide, you can very easily deduce what happens either by using the rule "acid + base --> salt + water" or just simply memorise what I got below!
C6H8O7(aq) + NaOH(s) --> NaC6H5O7(aq) + 3H2O(l)
Hope my answer has helped with your understanding of these areas of chemistry, and they are indeed hard concepts to master. Once again, thanks for being helpful in the community and if you have any further questions, please dont hesitate to ask!
Best Regards
Happy Physics Land