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Chemistry of Bread-Making

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    ChemistryOfBreadHandout.png

     

    The Chemistry of Bread Making

    Please read over “The Chemistry of Bread Making” handout. Use the information on this worksheet and the material on acid/base chemistry presented to you in lecture to answer the questions below. Show all work you use to derive your answers.

    1. In the baking of the bread, which molecules are acting as acids? As bases? Only consider the molecules fats, baking soda, baking powder, and ascorbic acid.

       

    1. If baking soda (sodium bicarbonate, NaHCO3) were to be added to water in the following proposed reactions:

      Note: Carbonic acid and bicarbonate have a reported pKa of 6.1 and 10.3 respectively.

      \[\ce{HCO3- + H2O ⇌} \nonumber\]

      1. Write in the predicted products of this reaction above.

         

      2. Will this reaction form an acidic, basic, or neutral solution? Explain in terms of the species present when the salt dissolves and conjugate acids/bases.

         

         

         

         

      1. Using your prediction for the reaction above, calculate the resulting pH of a water mixture if you add 5.2 g of baking soda to 500 mL of water. (Ignore the Na+ ion in Molarity calculations)

         

         

         

         

         

         

         

         

      2. If you add 5 mL of lemon juice (MW ascorbic acid = 176.12 g/mol, density ascorbic acid = 1.65 g/cm3, pka1 = 4.17) to your mixture, what is the reaction that occurs?

         

         

         

        1. Predict the which side the equilibrium lies on. Hint: Evaluate the strengths of acids & bases playing roll.

           

           

        2. Label the strongest acid and the strongest base. Label each entity with the corresponding pKa or pKb.

           

           

           

        3. Label the conjugate acid/base pairs.

           

           

           

    1. Given the reactions of baking soda and baking powder before and during the baking process:
        Baking Soda Baking Powder
      Before Baking \(\ce{HCO3- + H2O \leftrightarrow  H2CO3 + OH-}\) \(\ce{HCO3- + HA → CO2 + H2O + A-}\)
      During Baking \(\ce{HCO3- + H2O + heat → CO2 + H2O}\) \(\ce{HCO3- + H2O + heat → CO2 + H2O}\)
      1. If you want to make your baked goods “spongier” (less dense), should you use baking soda, or baking powder? Why?

         

         

         

      2. What do you think the label “double acting” on baking powder means?

         

         

    1. You really want to make muffins for you and your roommate(s), but all you have in your pantry is baking soda. Utilizing the information learned in this activity, what can you add to your baking mixture (flour, baking soda, water, etc.) to get nice, fluffy muffins?

       

       

       

    1. If the average pH of St. Louis tap water is 8.35, how much baking soda would be necessary to add to a 500mL solution to achieve a pH similar to that of tap water? Is that realistic with typical kitchen supplies?

       

       

       

       

       

       

       

       

       

    1. What do you think is neutralizing the mixture for the bread?

       

       

       

       

       

       

       

       

       

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