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DP IB Chemistry: HL

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Home / IB / Chemistry: HL / DP / Topic Questions / 18. Acids & Bases (HL only) / 18.2 Calculations Involving Acids & Bases / Structured Questions: Paper 2


18.2 Calculations Involving Acids & Bases

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Question 1a

Marks: 1
a)
Determine the Ka of benzoic acid using section 21 of the Data booklet.
[1]
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    Key Concepts
    Acid & Base Dissociation Constants
    Acid & Base Calculations

    Question 1b

    Marks: 1
    b)
    Using the Ka value for benzoic acid, state and explain its acidic character.
    [1]
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      Key Concepts
      Strong & Weak Acids & Bases

      Question 1c

      Marks: 5
      c)
      Benzoic acid has a solubility of 0.344 g / 100 g water at 293 K. Determine the hydrogen ion concentration and pH of saturated benzoic acid solution at this temperature.
      [5]
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        Key Concepts
        Acid & Base Calculations

        Question 1d

        Marks: 1
        d)
        What assumption is made in the calculation in part c)?
        [1]
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          Key Concepts
          Acid & Base Dissociation Constants

          Question 2a

          Marks: 3
          a)
          Nitric acid, HNO3, and hydrocyanic acid, HCN, can be made from ammonia. Hydrocyanic acid has a pKa of 9.21.
          Formulate equations for the dissociation of each acid and distinguish between the terms strong and weak in this context.
          [3]
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            Key Concepts
            Comparing Strong & Weak Acids

            Question 2b

            Marks: 2
            b)
            Write an expression for the acid dissociation constant, Ka, of hydrocyanic acid and calculate the Ka at 298 K.
            [2]
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              Key Concepts
              Acid & Base Dissociation Constants

              Question 2c

              Marks: 2
              c)
              Determine the hydrogen ion concentration and pH of 0.15 mol dm-3 hydrocyanic acid.
              [2]
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                Key Concepts
                Acid & Base Calculations

                Question 2d

                Marks: 2
                d)
                Write an expression to show the ionisation of the conjugate base of hydrocyanic acid and calculate it Kb value.
                [2]
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                  Key Concepts
                  Acid & Base Calculations
                  Relating Kw to Ka

                  Question 3a

                  Marks: 3
                  a)
                  Calculate the pH of a solution made by mixing 50.0 cm3 of 0.200 mol dm-3 HCl (aq) with 50.0 cm3 of 0.100 mol dm-3 NH3 (aq)

                  [3]

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                    Key Concepts
                    Acid & Base Calculations

                    Question 3b

                    Marks: 5
                    b)
                    A 0.100 mol dm-3 solution of NH3 (aq) contains 1.28 x 10-3 mol dm-3 in hydroxide ion.

                    i)
                    Determine the pH of the solution.

                    [3]

                    ii)
                    Comment on the relative base strength of 0.100 mol dm-3 NaOH (aq) compared to 0.100 mol dm-3 NH3 (aq)

                    [2]

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                      Key Concepts
                      Acid & Base Calculations

                      Question 3c

                      Marks: 3
                      c)
                      Determine the base dissociation constant, Kb for ammonia using the information in part b).

                      [3]

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                        Key Concepts
                        Acid & Base Calculations

                        Question 3d

                        Marks: 4
                        d)
                        The pH of pure water is 6.92 at 328 K and Kb for NH3 (aq) at this temperature is 1.80 x10-5.
                        Determine the pKa of [NH4+] at this temperature.

                        [4]

                          Assess your score
                            
                          Key Concepts
                          Acid & Base Calculations
                          Relating Kw to Ka


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