Problem PageQuestion A chemistry graduate student is given of a benzoic acid solution. Benzoic acid is a weak acid with . What mass

Problem PageQuestion A chemistry graduate student is given of a benzoic acid solution. Benzoic acid is a weak acid with . What mass of should the student dissolve in the solution to turn it into a buffer with pH ? You may assume that the volume of the solution doesn't change when the is dissolved in it. Be sure your answer has a unit symbol, and round it to significant digits.

Answers

Complete Question

A chemistry graduate student is given 125.mL of a 1.00M benzoic acid HC6H5CO2 solution. Benzoic acid is a weak acid with pKa = 4.2. What mass of KC6H5CO2 should the student dissolve in the HC6H5CO2 solution to turn it into a buffer with pH =4.63? You may assume that the volume of the solution doesn't change when the KC6H5CO2 is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits.

The mass would be  mass  of  KC_6H_5CO_2  = 54 g

Explanation:

   From the question we are told that

           concentration of benzoic acid is M_B = 1M

            The volume of benzoic acid is V_B = 125mL = 0.125L

            The value of the experimental parameter is pKa = 4.2

          The value of PH is PH =4.63

Generally the number of moles is mathematically represented as

             No of moles = concentration * volume  

                            N = M_B * V_B

Substituting values

                          N = 1 * 0.125 = 0.125 moles

 Generally PH is mathematically represented as

               PH = pKa + logfrac{[KC_6H_5CO_2]}{[HC_6H_5CO_2]}

Where [KC_6H_5CO_2] is the No of moles of KC_6H_5CO_2 and [HC_6H_5CO_2] is the number of moles of benzoic acid

              4.3 = 4.2 + logfrac{[KC_6H_5CO_2]}{0.125}

             4.63 - 4.2 = log frac{[KC_6H_5CO_2]}{0.125}

                           0.43 =log frac{[KC_6H_5CO_2]}{0.125}

                         10^{0.43} =frac{[KC_6H_5CO_2]}{0.125}

                         2.6915 *0.125 = [KC_6H_5CO_2]

                          [KC_6H_5CO_2]= 0.3364

Generally the number of moles is mathematically represented as

              No   of   moles  =  frac{Mass}{Molar  Mass}

For [KC_6H_5CO_2]

             0.3364 = frac{mass  of  KC_6H_5CO_2}{Molar  Mass  of   KC_6H_5CO_2 }

         Molar mass of KC_6H_5CO_2 = 160g/mole

         0.3364 * 160  =mass  of  KC_6H_5CO_2

         mass  of  KC_6H_5CO_2  = 54 g

           

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