Методическая разработка по английскому языку для студентов факультета химии и химической технологии " Simple Chemistry" Алматы 2017
WRITING IONIC EQUATIONS FOR REDOX REACTIONS (Examples )
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| WRITING IONIC EQUATIONS FOR REDOX REACTIONS (Examples )
Example 1: The reaction between chlorine and iron(II) ions Chlorine gas oxidises iron(II) ions to iron(III) ions. In the process, the chlorine is reduced to chloride ions. You would have to know this, or be told it by an examiner. In building equations, there is quite a lot that you can work out as you go along, but you have to have somewhere to start from! You start by writing down what you know for each of the half-reactions. In the chlorine case, you know that chlorine (as molecules) turns into chloride ions: The first thing to do is to balance the atoms that you have got as far as you possibly can: ALWAYS check that you have the existing atoms balanced before you do anything else. If you forget to do this, everything else that you do afterwards is a complete waste of time! Now you have to add things to the half-equation in order to make it balance completely. All you are allowed to add are: electrons water hydrogen ions (unless the reaction is being done under alkaline conditions - in which case, you can add hydroxide ions instead) In the chlorine case, all that is wrong with the existing equation that we've produced so far is that the charges don't balance. The left-hand side of the equation has no charge, but the right-hand side carries 2 negative charges. That's easily put right by adding two electrons to the left-hand side. The final version of the half-reaction is: Now you repeat this for the iron(II) ions. You know (or are told) that they are oxidised to iron(III) ions. Write this down: The atoms balance, but the charges don't. There are 3 positive charges on the right-hand side, but only 2 on the left. You need to reduce the number of positive charges on the right-hand side. That's easily done by adding an electron to that side: Combining the half-reactions to make the ionic equation for the reaction What we've got at the moment is this: It is obvious that the iron reaction will have to happen twice for every chlorine molecule that reacts. Allow for that, and then add the two half-equations together. But don't stop there!! Check that everything balances - atoms and charges. It is very easy to make small mistakes, especially if you are trying to multiply and add up more complicated equations. You will notice that I haven't bothered to include the electrons in the added-up version. If you think about it, there are bound to be the same number on each side of the final equation, and so they will cancel out. If you aren't happy with this, write them down and then cross them out afterwards! жүктеу/скачать 422,31 Kb. Достарыңызбен бөлісу:
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