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    Inorganic & Physical Chemistry numerical Problems

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    1. Combustion of 5.13g of ibuprofen a widely used painkiller produces 14.224g CO2, 4.029g H2O. Ibuprofen contains only carbon hydrogen and oxygen atoms. If the molecular weight of ibuprofen is liss than 400g/mol determine the molecular formula.

    2. A. From the data on the last page calculate the free energy change for the reaction at 25C
    2CH4(g) --->C2H4(g) + 2H2(g)

    B. At what temperature will the reaction go from spontaneous to non-spontaneous?

    3. Give the electronic configuration for the following atoms or ions.
    a) Cr3+
    b) Cu
    c) Se2-

    4. Complete the molecular orbit energy diagram for CO and determine its bond order. s CO paramagnetc of diamagnetic?

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    1. Because masses of carbon and hydrogen are conserved, we can find the moles of each in the sample from the masses of CO2 and H2O

    14.224 g CO2 x (1 mol CO2 / 44.01 g CO2) x (1 mol C / 1 mol CO2)
    = 0.3232 mol C

    4.029 g H2O x (1 mol H2O / 18.02 g H2O) x (2 mol H / 1 mol H2O)
    = 0.4472 mol H

    To find the moles of O, we must first find the masses of C and H in the sample

    0.3232 mol C x 12.01 g C / 1 mol C = 3.8816 g C

    0.4472 mol H x 1.008 g H / 1 mol H = 0.4508 g H

    and determine the mass of O by difference, as below

    5.13 g sample - (3.8816 g C + 0.4508 g H) = 5.13 - 4.3324 = 0.7976 g O

    The moles of O, therefore, are
    0.7976 g O x (1 mol O / 16.00 g O) = 0.0499 mol O

    Hence the molar ratios of C-to-O and H-to-O are
    nC / nO = 0.3232 mol C / 0.0499 mol O = 6 mol C / 1 mol O (approx)
    nH / nO = 0.4472 mol H / 0.0499 mol O = 9 mol H / 1 mol O (approx)

    giving an empirical formula of C6H9O

    The apparent molar mass based on this empirical formula is: (12x6) + (1x9) + 16 = 97

    Dividing the actual molar mass (206.29 for Ibuprofen) by apparent molar mass

    Actual molar mass / Apparent molar mass = 206.29 / 97 = 2 (approx)

    So multiplying empirical formula's subscripts by 2, the molecular formula is:

    2. Insufficient data!
    (A) Enthalpy change (∆H) and entropy change (∆S) values for this reaction needs to be provided.
    Then the formula that you use to find change is free energy is: ∆G = ∆H - T∆S

    (B) For spontaneous reaction, ∆G < 0
    So for transition from spontaneous to non-spontaneous reaction,
    ∆G = 0 or ∆H - T∆S = 0

    Again if you know ∆H and ∆S, you can find the temperature T.

    3. (a) Cr: [Ar] 3d5 4s1, Cr3+: [Ar] 3d3
    (b) Cu: [Ar] 3d10 4s1
    (c) Se: [Ar] 3d10 4s2 4p4, Se2-: [Ar] 3d10 4s2 4p6

    4. MO diagram of CO:

    From this MO diagram:

    Bond order = (numbers of electrons in bonding orbitals - number of electrons in anti-bonding orbitals) / 2 = (8 - 2) / 2 = 3

    As CO has no unpaired electrons, CO is diamagnetic.

    5. Here is what the quantum number set stands for:

    (i) Principle Quantum Number is the energy level (shell level, n). The larger the principle quantum number, the larger the energy and size of electron orbital.

    (ii) The second quantum number is the azimuthal quantum number which designates the sub-shell. The oribital shapes l = 0 (s), l = 1 (p), l = 2 (d), l = 3 (f).
    For each new shell (principle quantum number) there exists an additional sub-shell.

    For example n = 1, means that there is only one subshell l = 0.

    Thus the range is l = 0 to n-1.

    (iii) The third quantum number is the magnetic quantum number (ml) that designates the exact orbital within a sub-shell. Sub-shells can have more than ...

    Solution Summary

    Detailed answers to a set of inorganic and physical chemistry problems, clearly showing all steps and offering adequate explanations.