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Homework Help: Electric net charge problem

  1. Jan 13, 2007 #1
    Suppose a 1.68 g nugget of pure gold has zero net charge. What would be its net charge after it has 1% of its electrons removed?

    Answer in C
    Electric charge of proton = 1.602e-19 C 1.673e-27 kg
    Electric charge of electron = -1.602e-19 C 9.109e-31 kg
    Electron charge of neutron = 0 1.675e-27 kg

    I have attempted one answer of 1.602e-21 C, but I am really confused at how to obtain the solution. I know this is supposed to be an easy problem, but I am just confused. Any assistance would be greatly appreciated.
  2. jcsd
  3. Jan 13, 2007 #2
    How many electrons are in 1.68 grams?
  4. Jan 13, 2007 #3
    The first thing that is needed is to convert 1.68 g gold into moles, which comes out to 1.68 / 196.97 = 0.0085 mol gold.

    Since it starts off as a neutral sample, there must be exactly one electron for every proton present. Every gold atom has 79 protons, which means each atom would have initially 79 electrons.

    So, convert the moles of gold into atoms by (0.0085 mol)*(6.022*10^23 atoms/mol) = 5.14 x 10^21 atoms of gold. This implies that there are (5.14 x 10^21)*(79 protons/atom)*(1 electron/1 proton) = 4.058 x 10^23 electrons present. One percent of these gone corresponds to (1-0.01)*(4.058 x 10^23) = 4.02 x 10^23 electrons.

    Now, find the charge on the protons and electrons
    4.023 x 10^23 electrons*(-1.602e-19 C) = -64453 C
    4.064 x 10^23 protons*(1.602e-19 C) = 65104 C

    Add the charges together to get +651 C

    Concept check: This makes sense because if the sample is losing electrons, the net charge of the sample should increase
    Last edited by a moderator: Jan 20, 2007
  5. Jan 13, 2007 #4


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    Chemhelper. Please note that it is against PF policy to post full solutions to questions in the homework forums. See FAQ here and PF global guidelines here
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