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Calculate the pH for 0.001 M HCl.

Chemistry

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Answer

II and III\text{II and III}

Step-by-step solution

5 steps

let's evaluate each statement to determine which are correct.

Statement I: The pH of 0.001 M H₂SO₄(aq) and 0.001 M HCl(aq) are the same.

  1. Calculate the pH for 0.001 M HCl.

    HCl is a strong monoprotic acid, so it dissociates completely.

    [H+]=0.001 M=10−3 M[\text{H}^+] = 0.001 \text{ M} = 10^{-3} \text{ M} pH=−log⁡[H+]=−log⁡(10−3)=3\text{pH} = -\log[\text{H}^+] = -\log(10^{-3}) = 3
  2. Calculate the pH for 0.001 M H₂SO₄.

    H₂SO₄ is a strong diprotic acid. For dilute solutions, both protons are considered to dissociate completely.

    H2SO4→2H++SO42−\text{H}_2\text{SO}_4 \to 2\text{H}^+ + \text{SO}_4^{2-}

    So, for 0.001 M H₂SO₄, the concentration of H+\text{H}^+ is approximately 2×0.001 M=0.002 M=2×10−3 M2 \times 0.001 \text{ M} = 0.002 \text{ M} = 2 \times 10^{-3} \text{ M}.

    pH=−log⁡(2×10−3)=3−log⁡(2)≈3−0.301=2.699\text{pH} = -\log(2 \times 10^{-3}) = 3 - \log(2) \approx 3 - 0.301 = 2.699

    Since 3≠2.6993 \neq 2.699, the pH values are not the same.
    Therefore, Statement I is incorrect.

    Statement II: The pOH of 0.001 M NaOH(aq) is 3.

  3. Determine the concentration of OH−\text{OH}^-.

    NaOH is a strong base, so it dissociates completely.

    NaOH→Na++OH−\text{NaOH} \to \text{Na}^+ + \text{OH}^-

    For 0.001 M NaOH, [OH−]=0.001 M=10−3 M[\text{OH}^-] = 0.001 \text{ M} = 10^{-3} \text{ M}.

  4. Calculate the pOH.

    pOH=−log⁡[OH−]=−log⁡(10−3)=3\text{pOH} = -\log[\text{OH}^-] = -\log(10^{-3}) = 3

    Therefore, Statement II is correct.

    Statement III: The ionic product of water, Kw, is temperature dependent.

    The autoionization of water is an endothermic process:

    H2O(l)⇌H+(aq)+OH−(aq)\text{H}_2\text{O(l)} \rightleftharpoons \text{H}^+\text{(aq)} + \text{OH}^-\text{(aq)}

    According to Le Chatelier's principle, an increase in temperature shifts the equilibrium to the right, increasing the concentrations of both H+\text{H}^+ and OH−\text{OH}^-. Since Kw=[H+][OH−]K_w = [\text{H}^+][\text{OH}^-], KwK_w increases with temperature.
    Therefore, Statement III is correct.

    Statement IV: The pKb of 0.010 M NH₃ solution is greater than 7. (kb of NH₃ = 1.8 x 10⁻⁵)

  5. Calculate the pKb from the given KbK_b.

    The pKb is a constant for a given base and does not depend on its concentration.

    pKb=−log⁡(Kb)\text{pKb} = -\log(K_b) pKb=−log⁡(1.8×10−5)\text{pKb} = -\log(1.8 \times 10^{-5}) pKb=5−log⁡(1.8)\text{pKb} = 5 - \log(1.8) pKb≈5−0.255=4.745\text{pKb} \approx 5 - 0.255 = 4.745

    Since 4.745 is not greater than 7, the statement is incorrect.
    Therefore, Statement IV is incorrect.

    Conclusion:
    Statements II and III are correct.

    The final answer is II and III\text{II and III}.

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