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    what is the oxidation number of.

    Asked Nov 18, 2009, 04:39 PM 9 Answers


    what is the oxidation number of

    Mn in MnCl2 --> +2
    Mn in MnO4^- ---->
    S in K2S4O6 ----------> +10
    Cl in HCl ------>+1

    I couldn't do (Mn in MnO4^- ---->) this one and also i am not sure on third one either..
    Please help me ohh.. do i have to multiply coefficant to each molecule before looking for oxidation number?

    Last edited by sarah1004; Nov 18, 2009 at 04:45 PM.
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    Perito's Avatar
    Perito Posts: 3,139, Reputation: 150
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    #2

    Nov 18, 2009, 08:17 PM

    Mn in MnCl2. Cl is always -1. Therefore, Mn must be +2.

    Oxygen is always -2

    S is usually -2

    H is always +1

    Since Oxygen is always -2, the formal charge from the four oxygen atoms must be -2 x 4 = -8. MnO4- has a negative charge on it, Therefore -8 + 7 = -1, so its oxidation number must be +7.

    Yes, you do have to multiply the coefficient (not coefficant) of each atom by its formal oxidation number
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    sarah1004's Avatar
    sarah1004 Posts: 107, Reputation: 1
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    #3

    Nov 18, 2009, 09:37 PM
    Mn in MnCl2 --> +2
    Mn in MnO4^- ----> +7
    S in K2S4O6 ----------> +13
    Cl in HCl ------>+1

    are these are correct?
    but I cannot find Mn in MnO4^- this part on equation...

    THanks
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    Perito's Avatar
    Perito Posts: 3,139, Reputation: 150
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    #4

    Nov 19, 2009, 04:45 AM
    Quote Originally Posted by sarah1004 View Post
    Mn in MnCl2 --> +2
    Mn in MnO4^- ----> +7
    S in K2S4O6 ----------> +13
    Cl in HCl ------>+1

    are these are correct?
    but i cannot find Mn in MnO4^- this part on equation...
    Why simply repeat the question?

    Mn in MnCl2 is +2 because each Cl is -1. That is correct.

    Mn in MnO4- is +7 That is correct.

    S in K2S4O6. Sulfur is definitely NOT +13. That is not correct.

    IF sulfur were +13, this is the calculation that you'd perform:

    K: +1, 2 atoms, total formal charge = +2
    O: -2, 6 atoms, total formal charge = -12
    S: +13, 4 atoms, total formal charge = +52.

    52 + 2 - 12 = 42. That is not a neutral molecule! Try again with K = +1 and O = -2.

    Cl in HCl. Chlorine is definitely not +1 in this molecule. In this molecule, H has an oxidation state of +1. You can figure it out from there.
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    sarah1004's Avatar
    sarah1004 Posts: 107, Reputation: 1
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    #5

    Nov 19, 2009, 10:51 AM
    S in K2S4O6
    If K is +1 and O is -2

    +2 + -12 = -10

    but that's S4.. so... It should be +2 or +3... I guess...
    and Cl in HCl is +1

    Thank
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    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #6

    Nov 19, 2009, 10:57 AM

    Actually, since it is thiosulfate we are dealing wit, you'll come up with an unusual answer. Actually doing the calculation:

    K2S4O6 has a total charge of zero
    K is +1, so 2K is +2
    O is -2, so 6O is -12
    Total of those two gives -10

    That means S4 must me +10 for the whole to be 0.
    So, that makes S be 10/4 = 2.5 (Surprising huh? A fraction!)

    But actually, you have a peroxide bonding within the O atoms which have an oxidation state of -1 instead of -2. But that's not for now, but late on.

    Next, HCl has no charge, so the charge of H and Cl must add up to zero.
    H is +1.
    If Cl is +1 too, the total makes 2+, which is not right!
    So, what is the Oxidation state (or number) of Cl in HCl?
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    sarah1004's Avatar
    sarah1004 Posts: 107, Reputation: 1
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    #7

    Nov 19, 2009, 11:02 AM
    Cl is -1
    I hope it is!

    So, S is +1?
    Thanks
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    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #8

    Nov 19, 2009, 11:04 AM

    At last!
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    sarah1004's Avatar
    sarah1004 Posts: 107, Reputation: 1
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    #9

    Nov 19, 2009, 11:14 AM
    Thank you!!

    Can you help me on this..
    A piece of a metal 34.9g was heated to about 95C and them added to 550g water with the initial temperature of 28.2C. If the final temperature of the water and the metal is 31.2C, calculate the specific heat of the metal.

    Do we have any special formula?

    I think its
    Heat lost/mass of metal*change in temperature of metal.

    so its like
    X/34.9g*(31.2-28.2C)

    I am not sure... but.. helpe
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    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #10

    Nov 19, 2009, 11:23 AM

    Hmm, nope. In such experiments, you don't know the specific heat capacity of the metal, which is the amount of energy required to raise the temperature of 1 kilogram of a substance by 1 degree Kelvin.

    The formula is

    Where m is the mass, c the specific heat capacity, theta the change in temperature, and Q the heat involved.

    The specific heat capacity of water is usually given.

    You have the mass of the water, the temperature rise of the water and presumably the specific heat capacity of the water.

    You can find the amount of heat transferred from the metal to the water.

    Then, using again the same formula, but using the values for the metal, you have the energy Q, the mass m, the change in temperature. Then, you can solve for c.
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