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7.7: Unit 7 Practice Problems

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    Question 1.

    Given the molarity, find the normality of the acid or base.

    0.24 M NaOH

    1.2 M H3PO4

    0.73 M H2SO4

    Answer

    0.24M x 1 = 0.24N

    1.2M x 3 = 3.6N

    0.73M x 2 = 1.5N 

    Given the normality, find the molarity of the acid or base.

    1.5N HCl

    0.84N Mg(OH)2 

    0.9N  NH4OH

    Answer

    1.5N / 1 = 1.5M

    0.84N / 2 = 0.42M

    0.9N / 1 = 0.9M

    Question 2. 

    Given the H+ concentration, find the OH- concentration, and the pH.  

    [H+] = 0.0046 M

    [H+] = 3.57 x 10-8 M

    Answer

    Remember the following formulas   [H+] x [OH-] = 10-14M              pH = -log [H+]

    [H+] = 0.0046 M           OH- = 10-14/0.0046 = 2.2x10-12 M                 pH = -log(0.0046) = 2.3

    [H+] = 3.57 x 10-8 M      OH- = 10-14/3.57x10-8 = 2.8 x 10-7 M           pH = -log(3.57x10-8 ) = 7.4

    Question 3. 

    Given the pH, find the H+ concentration and the OH- concentration.  

    pH = 12.97

    pH = 1.3

    Answer

    Remember the following formulas      [H+] = 10-pH              [H+] x [OH-] = 10-14M   

    pH 12.9            [H+] = 10-12.9 = 1.26 x 10-13M           [OH-] = 10-14/1.26x10-13 = 0.0794 M

    pH 1.3              [H+] = 10-1.3 = 0.050 M                     [OH-] = 10-14/0.050 = 2.0 x 10-13M

    Question 4. 

    Given the [OH-] concentration find the pH and state whether the concentration is acidic basic or neutral.  

    [OH-] = 4.6 x 10-2 M

    [OH-] = 1.0 x 10-7 M

    [OH-] = 5.2 x 10-9 M

    Answer

    Remember the following formulas   [H+] x [OH-] = 10-14M              pH = -log [H+]

    [OH-] = 4.6 x 10-2 M     [H+] = 10-14/4.6x10-2 = 2.2 x 10-13 M           pH = -log(2.2 x 10-13) = 12.6             pH above 7 is basic

    [OH-] = 1.0 x 10-7 M     [H+] = 10-14/1.0x10-7 = 1.0 x 10-7 M            pH = -log(1.0 x 10-7) = 7.0                pH of 7 is neutral

    [OH-] = 5.2 x 10-9 M     [H+] = 10-14/5.2x10-9 = 1.9 x 10-6 M             pH = -log( 1.9 x 10-6) = 5.7              pH below 7 is acidic

    Question 5. 

    Write the balanced chemical equation for the neutralization of phosphoric acid and magnesium hydroxide.  Then state whether the resulting solution will be slightly acidic, slightly basic, or neutral.  

    Answer

    2H3PO4   +   3Mg(OH)2 →  Mg3(PO4)2 + 6H2O

    weak acid + strong base = slightly basic 

    Question 6. 

    20.5mL of 0.25M sulfuric acid is used to titrate 34.0mL of sodium hydroxide.  What is the normality and molarity of sodium hydroxide?

    Answer

    NaVa = NbVb

    Since the formula for sulfuric acid is H2SO4   Na = 0.25M x 2 = 0.50N

    (0.50N)(20.5mL) = (Nb)(34.0mL)

    Nb = 0.30N  

    Since the formula for sodium hydroxide is NaOH   Mb = 0.30N / 1 = 0.30M

    Question 7.

    Most toilet cleaners contain acid to help remove mineral deposits from the bowl.  If 38mL of toilet cleaner takes 26mL of 0.24N NaOH to titrate it, what is the normality of the toilet cleaner?

    Answer

    NaVa = NbVb

    (Na)(38mL) = (0.24N)(26mL)

    Na = 0.16N

    7.7: Unit 7 Practice Problems is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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