60 coulombs would produce 60 times this amount. If 96500 coulombs give 108 g, then 1 coulomb would give 108 divided by 96500 g. Note: If your maths is really bad, so that you aren't happy about simple proportion sums, then think of it like this: So, if 96500 coulombs give 108 g of silver, all you have to do is to work out what mass of silver would be produced by 60 coulombs. Just as with any other calculation from an equation, write down the essential bits in words:ġ mol of electrons gives 1 mol of silver, Ag. Now look at the equation for the reaction at the cathode: The first thing to do is to work out how many coulombs of electricity flowed during the electrolysis. In fact, you may well have done them as a part of whatever course you did before you started doing A level.Ĭalculate the mass of silver deposited at the cathode during the electrolysis of silver nitrate solution if you use a current of 0.10 amps for 10 minutes.į = 9.65 x 10 4 C mol -1 (or 96500 C mol -1 if you prefer). Using the Faraday constant in calculationsĮlectrolysis calculations are no more difficult than any other calculation from an equation. You will normally find this towards the end of the syllabus. Check your syllabus to find out what is contained in the Data Booklet you are likely to be given. Note: I have said three times that a piece of information is likely to be given to you in an exam, but you need to be sure.
Whenever you have an equation in which you have 1 mole of electrons, that is represented in an electrical circuit by 1 faraday of electricity - in other words, by 96500 coulombs. Notice the small "f" when it is used as a unit. This is another number you are unlikely to have to remember.
For exam purposes, the value of the Faraday constant is usually taken as 9.65 x 10 4 C mol -1 (coulombs per mole).
#CL CHARGE IN COLOUMB HOW TO#
The calculation just shows you how to work it out if you have to, but doesn't give the normally-used value. The numbers we are using here are rounded off. We have just used that without actually stating it - it is basically obvious! You may come across the formula F = Le, where F is the Faraday constant, L is the Avogadro constant and e is the charge on an electron (in terms of the number of coulombs it carries). This value is known as the Faraday constant.
That means the 1 mole of electrons must carry You would also be given that in an exam if you needed to use it. If you ever needed to use it in an exam, you would be given the value.ġ mole of electrons contains the Avogadro constant, L, electrons - that is 6.02 x 10 23 electrons. The charge that each electron carries is 1.60 x 10 -19 coulombs. For calculation purposes, we need to know how to relate the number of moles of electrons which flow to the measured quantity of electricity. (60 minutes in each hour 60 seconds in each minute.)Įlectricity is a flow of electrons. If you are given a time in minutes or hours or days, then you must convert that into seconds before you do anything else.įor example, if a current of 2 amps flows for an hour, then: Number of coulombs = current in amps x time in seconds That means that you can work out how much electricity has passed in a given time by multiplying the current in amps by the time in seconds. If a current of 1 amp flows for 1 second, then 1 coulomb of electricity has passed. The coulomb is a measure of the quantity of electricity. Make sure you really understand the next bit. The Faraday constant is the single most important bit of information in electrolysis calculations. This page looks at how to do routine electrolysis calculations.
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