Chlorine is slowly passed into a solution that has 0.100 mol of potassium bromide and 0.100 mol of…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Chlorine is slowly passed into a solution that has of potassium bromide and of potassium iodide. The iodide ion is oxidised first, and only when it is all used up does the bromide ion react. Each mole of Cl2 oxidises 2 mol of halide. Take the molar mass of I2 as and of Br2 as . Find the volume of chlorine at and that just oxidises all the iodide, the volume that oxidises both halides, and the masses of iodine and bromine formed.
Need a reminder? The key ideaShow
A halogen oxidises the halide ion of another halogen when the cell potential is positive. The standard electrode potentials are F2 V, Cl2 V, Br2 V and I2 V. Work in moles: grams divided by molar mass, then use the ratios of the equation. At 273 K and 1 atm, 1 mol of gas fills 22.4 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.
Plan. The order follows the potentials: I2 is V, Br2 is V, so iodide is the easier to oxidise.
Step 1. The iodide. of needs of Cl2. The volume is . It gives of I2.
Step 2. The bromide. of needs another of Cl2. The total is , or .
Step 3. The masses. Iodine: . Bromine: .
Answer: , , of iodine and of bromine.
Check. The colour first turns brown (iodine) and later red-brown (bromine). The two stages need equal volumes of chlorine.
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