holder and stand
11 Thermometer
12 Funnel
13 Graduated cylinder, 100 ml
14 Squeeze bottle for deionized water
15 Tissue
16 Weighing paper
17 Spatula
18 Stirring hot plate with stirring bars
1.4 Reagents and Materials
1 Citric acid, monohydrate. MW = 210 g mole−1
2 KOH, 0.5 N
3 HCl, 0.5 N
4 HCl, 0.001 N
5 Sprite® (Coca Cola Company) or comparable lemon‐flavored soda
6 Selected vegetables, e.g. fresh and canned tomatoes
7 Calibration buffers, pH 2 and 4
1.5 Procedures
1.5.1 Determining the pH of a Solid Food [5]
1 Cut a fresh tomato into small cubes and blend in a blender until a uniform slurry is formed, measure the temperature of the slurry.
2 Calibrate your pH meter.
3 Measure the pH of the slurry.
4 Centrifuge an aliquot of the slurry for 10 minutes at maximum speed.
5 Measure the pH of the supernatant.
6 Repeat Steps 1 through 5 using canned tomatoes.
1.5.2 Preparation of a Buffer and Determination of Buffer Capacity
1 Calculate the amounts of citric acid monohydrate and 0.5 N KOH required to prepare 200 ml of 0.05 M citrate buffer, pH 3. Note: Even though citric acid is a triprotic acid, calculations for this pH range are made using pKa = 3.06.
2 Prepare 200 ml of the buffer.
3 Measure the pH of your buffer. Is it 3.0? If not, can you explain why?
4 Determine the buffer capacity of your buffer in the alkaline direction by titrating a 100 ml aliquot with 0.5 N KOH. Express buffer capacity as the number of moles of OH− required to increase the pH of 1 l of the buffer by 1 pH unit.
5 Repeat Step 4 using 0.001 N HCl in place of the citrate buffer, i.e. determine the buffer capacity of 0.001 N HCl.
6 Determine the buffer capacity of your buffer and 0.001 N HCl by calculation. Compare your experimental results with your calculated answers. Explain any discrepancies between experimental and calculated values.
7 Determine the buffer capacity of Sprite® in the same way you did for your citrate buffer (Step 4 above).
1.6 Problem Set
1 The Ka for the weak acid HA is 4.0 × 10−6. What is the pH of a 0.01 M solution of this acid? What is its pKa?
2 How many grams of acetic acid and sodium acetate are required to prepare 1.0 l of 0.5 M acetate buffer, pH 4.5? The pKa for acetic acid is 4.75.
3 Explain carefully how to prepare 1.0 l of 0.05 M phosphate buffer, pH 7.0 from NaH2PO4 .H2O and 1.0 N NaOH or 1.0 N HCl. The molecular weight of sodium phosphate monohydrate monobasic is 138 g mole−1. The pKa2 for H3PO4 is 7.21. Hint: To determine whether you will need to add NaOH or HCl, you need to calculate the pH of a 0.05 M solution of NaH2PO4.
4 Preparation of buffers using published tables.Using Tables III.2a, III.2b, and III.2c in Appendix III, describe carefully how you would prepare 1 l of 0.1 M acetate buffer, pH 5.2 and 1 l of 1/15 M phosphate buffer, pH 7.6.Using the Henderson–Hasselbalch equation (shown below), calculate the theoretical pH of these 2 buffers. Explain why the calculated pHs are not exactly the same as the pHs shown in the Appendix table.
1.7 References
1 1 FDA (2019). Acidified & low‐acid canned foods guidance documents & regulatory information [Internet]. FDA [cited 2020 Mar 5]. http://www.fda.gov/food/guidance‐documents‐regulatory‐information‐topic‐food‐and‐dietary‐supplements/acidified‐low‐acid‐canned‐foods‐guidance‐documents‐regulatory‐information (accessed 5 March 2020).
2 2 Bartek Ingredients, Inc (2020). Self teaching guide for food acidulants ‐ Google search [Internet]. [cited 2020 Mar 5] p. 37. https://www.google.com/search?q=Self+teaching+guide+for+food+acidulants&rlz=1C1EJFC_enUS825US876&oq=Self+teaching+guide+for+food+acidulants&aqs=chrome..69i57j69i60.2887j0j4&sourceid=chrome&ie=UTF‐8 (accessed 5 March 2020).
3 3 USDA ARS (2020). pH of selected foods [Internet]. [cited 2020 Mar 5]. https://pmp.errc.ars.usda.gov/phOfSelectedFoods.aspx (accessed 5 March 2020).
4 4 Bennion, M. (1980). The Science of Food . San Francisco: Harper & Row. 598 p.
5 5 AOAC Official Method 981.12 (1982). pH of Acidified Foods . AOAC International.
1.8 Suggested Reading
1 Lindsay, R.C. (2017). Food additives. In: Fennema’s Food Chemistry , 5e (eds. S. Damodaran and K.L. Parkin ), 803–864. Boca Raton: CRC Press, Taylor & Francis Group.
2 Segel, I.H. (1976). Biochemical Calculations: How to Solve Mathematical Problems in General Biochemistry , 2e. New York: Wiley. 441 p.
Answers to Problem Set
1 pH = 3.7; pKa = 5.4.
2 14.68 g sodium acetate; 19.26 g acetic acid.
3 Use NaOH to adjust pH; dissolve 6 g NaH2PO4 (or 6.9 g NaH2PO4·H2O) in water (~900 ml); using pH meter, titrate to pH 7.0 with 1.0 N NaOH; transfer to a volumetric flask and dilute to 1 l.
4 a)pH 5.2 acetate buffer: mix 768 ml 0.1 M sodium acetate and 232 ml acetic acid. pH 7.6 phosphate buffer: mix 128 ml 1/15 M KH2PO4 and 872 ml 1/15 M Na2HPO4.b)Calculated pHs: Acetate buffer = 5.27; Phosphate buffer = 8.04.
2 Chemical Leavening Agents
2.1 Learning Outcomes
After completing this exercise, students will be able to:
1 Write balanced chemical equations showing the production of CO2 in various chemical leavening systems.
2 Determine, experimentally, the rates of CO2 release from selected leavening systems.
3 Select a chemical leavening system suitable for making biscuits, muffins, and other baked products.
4 Use the ideal gas law to calculate the volume of available CO2 in a leavening system.
5 Calculate the weight of a given leavening acid required to neutralize a given amount of NaHCO3.
2.2 Introduction
Leavening is derived from the Latin word levo which means raising or making light. Batters