A 2.98g copper penny has a positive charge of 31.8uC. What fraction of its electrons has it lost? (Assume that natural copper has an atomic mass number of 63.5.)Thanks!
Let's start by finding out how many electrons you would expect to find in a 2.98 gram copper penny, assuming all the atoms were electrically neutral. Copper is element 29 on the periodic table, so each neutral atom bears 29 electrons. 2.98 g x (1 mol Cu / 63.5 g Cu) x (29 mol e- / 1 mol Cu) x (6.022x10^23 e- / 1 mol e-) = 8.20x10^23 e- Now let's figure out how many electrons would have to be lost to give the penny a charge of 31.8 uC. Keep in mind that each electron has a charge of -1.60x10^-19 C, so the penny becomes that amount more positive for each electron lost. 31.8 uC = 31.8x10^-6 C 31.8x10^-6 C x (1 e- / 1.60x10^-19 C) = 1.99x10^14 electrons Now figure out what fraction of a penny's total electrons is represented by 1.99x10^14. 1.99x10^14 e- / 8.20x10^23 = 2.43x10^-10 or 0.000 000 000 243. Put another way, that means the penny only lost 1 out of every 4.12 billion electrons. I hope that helps. Good luck!
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