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Note: Don't worry too much if you get this wrong and choose to transfer 24 electrons instead. All that will happen is that your final equation will end up with everything multiplied by 2. Your examiners might well allow that.
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The multiplication and addition looks like this:
Now you will find that there are water molecules and hydrogen ions occurring on both sides of the ionic equation. You can simplify this to give the final equation:
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Note: You have now seen a cross-section of the sort of equations which you could be asked to work out. Now you need to practice so that you can do this reasonably quickly and very accurately! Aim to get an averagely complicated example done in about 3 minutes.
If you want a few more examples, and the opportunity to practice with answers available, you might be interested in looking in chapter 1 of my book on Chemistry Calculations.
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Reactions done under alkaline conditions
Working out half-equations for reactions in alkaline solution is decidedly more tricky than those above. You are less likely to be asked to do this at this level (UK A level and its equivalents), and for that reason I've covered these on a separate page (link below). It would be worthwhile checking your syllabus and past papers before you start worrying about these!