Chemistry

If a current of 2.5A flows for 2hrs
45mins through a water voltameter.
Determine the volume of
hydrogen gas at s.t.p. [molar volume
of gasesat s.t.p = 22.4dm3.?

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  1. 2.75Hr*(60min/Hr)*(60s/min)=9,900s

    C=charge=current*time(s)=2.5A*9,900s=24750 C

    Faraday's constant=9500 C=1 mole

    24750*(mole/9500)=0.25648moles

    1 mole=22.4L at STP

    0.25648*22.4=5.74L

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  2. 5.74dm3=5.74L

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  3. seconds = 2 (3600) + 45 * 60 = 9900 seconds
    coulombs = current * time = 2.5 * 9900 = 24750 Coulombs
    How many electrons?
    24750 Coulombs ( 1 electron / 1.6*10^-19 coulombs)
    = (2.475 /1.6) 10^23 electrons
    Each H+ needs one electron so each H2 molecule needs two
    do we get 7.73 * 10^22 H2 molecules
    How many mols is that?
    6 * 10^23 molecules/mol
    so
    7.73*10^22 molecules ( 1 mol / 6*10^23 molecules) = 0.129 mol
    0.129 mol * 22.4 liter/mol = 2.9 liters

  4. Check arithmetic. I did that fast.

  5. an A (ampere) is a Coulomb of charge per second
    ... there are 9.5E4 Coulombs in a mole of electrons

    each mole of H2 requires two moles of electrons

    moles elec = 2.5 * 2.75 * 60 * 60 / 9.5E4

    calculate moles elec , divide by two for moles of H2

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  6. but Anon you need 2 mols of electrons for one mol of H2

  7. The correct answer is 2.87 L.
    2.75 x 60 x 60 x 2.5 = 24,750
    96,485 C will release 22.4/2 = 11.2 L H2 @ stp.
    11.2 L x (24,750/96,485) = 2.87 L H2 @ stp.

  8. So, sorry. I didn't pay ful l attention. It's H2 so 1 atom contains 2 electrons. So, 1 mole of a H2 gas at STP will contain 2 moles of electrons.

    2.75Hr*(60min/Hr)*(60s/min)=9,900s

    C=charge=current*time(s)=2.5A*9,900s=24750 C

    Faraday's constant=9500 C=1 mole

    24750*(mole/9500)=0.25648moles

    *****Correction

    1 mole= 2 moles of e^-=22.4L at STP

    0.25648 moles of e^-*(22.4L/2 moles of e^-)=2.87=2.9L

    All of the calculations that gave you 2.9L are correct.

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