MediumChemistryHigh School (11–12)ElectrochemistryNumerical

Three cells are joined in series. One holds silver nitrate solution, one holds zinc sulphate…

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Three cells are joined in series. One holds silver nitrate solution, one holds zinc sulphate solution and one holds a melt that contains $\text{Al}^{3+}$ ions. The silver cell gains $1.62\ \text{g}$ of silver. Use $M(\text{Ag}) = 107.9\ \text{g/mol}$ , $M(\text{Zn}) = 65.4\ \text{g/mol}$ and $M(\text{Al}) = 27.0\ \text{g/mol}$ . Find the charge that passed, and the masses of zinc and aluminium deposited.

Need a reminder? The key ideaShow

$Q = It$ , with the time in seconds, and $F = 96500\ \text{C/mol}$ . For $\text{M}^{z+} + ze^- \rightarrow \text{M}$ , the mass is $m = \dfrac{Q}{zF}M$ . The same charge through different cells gives masses in the ratio of $M/z$ . At $273\ \text{K}$ and $1\ \text{atm}$ one mole of gas is $22.4\ \text{L}$ .

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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