atmospheres (atm)V = volume in liters (l)n = number of moles of gasR = 0.0821 (l) (atm) (mol−1) (K−1)T = temperature in K
2 Volume of 1 mole of CO2 under standard conditions = 22.40 l.
3 Standard temperature and pressure for gases: T = 273 K; P = 1 atm.
4 Baking soda content of baking powder: 28% NaHCO3 (w/w).
5 Formula weight of NaHCO3 = 84.01.
6 Molecular weight of CO2 = 44.0.
2.8 References
1 1 Van Wazer, J.R. and Arvan, P.G. (1954). Chemistry of leavening. Milling Production February–March: 3–7.
2 2 Heidolph, B.B. (1996). Designing chemical leavening systems. Cereal Foods World 41 (3): 118–126.
3 3 Gardner, W.H. (1966). Food Acidulants . Allied Chemical. 185 p.
4 4 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.
5 5 McGee, H. (2004). On Food and Cooking: The Science and Lore of the Kitchen . Completely rev. and updated. New York: Scribner. 884 p.
6 6 AACC method 2‐32 A (1995). Neutralizing value of acid‐reacting materials. In: Approved Methods of the AACC , 9e. St. Paul, MN: The American Association of Cereal Chemists.
7 7 Book, S.L. and Waniska, R.D. (2015). Leavening in flour tortillas. In: Tortillas (eds. L.W. Rooney and S.O. Serna‐Saldivar ), 159–183. St. Paul, MN: AACC International Press.
8 8 Bellido, G.G., Scanlon, M.G., Sapirstein, H.D., and Page, J.H. (2008). Use of a pressuremeter to measure the kinetics of carbon dioxide evolution in chemically leavened wheat flour dough. Journal of Agricultural and Food Chemistry 56 (21): 9855–9861.
9 9 Kichline, T.P. and Conn, T.F. (1970). Some fundamental aspects of leavening agents. Bakers Digest 44 (4): 36–40.
10 10 Conn, J.F. (1981). Chemical leavening systems in flour products. Cereal Foods World 26 (3): 119–123.
11 11 Penfield, M.P. and Campbell, A.M. (1990). Experimental Food Science , 3e. San Diego: Academic Press. 541 p. (Food science and technology).
2.9 Suggested Reading
1 Labaw, G.D. (1982). Chemical leavening agents and their use in bakery products. Bakers Digest. 56 (1): 16.
2 Robinson, J.K., McMurry, J., and Fay, R.C. (2019). Chemistry , 8e. Hoboken, NJ: Pearson Education, Inc. 1200 p.
Answers to Problem Set
1 Volume of CO2 = 99 ml
2 Fast‐acting acids dissolve rapidly, slow‐acting acids dissolve more slowly.
3 Bicarbonate has a high pKa, which means it will not dissociate until the pH is high.
4 Double‐acting powders allow release of some CO2 prior to baking which helps improve batter viscosity.
5 1.25 lb MCP.
6 Normality of vinegar = 0.833 N. It will take 12 ml vinegar to neutralize 100 ml of 0.1 N NaOH.
7 143 ml vinegar.
8 Two equations may be written: Monoprotic: Diprotic: The published value of 80 lies between 67 and 133. This suggests that the sodium bicarbonate reacts nearly completely with the first H on the H2PO4 − but only partially with the second, i.e. the diprotic reaction above does not go to completion.
9 1.72 l CO2.
10
11
12
13 A lactone is an ester formed from the reaction of a carboxyl group and an alcohol group on the same molecule. Glucono‐delta‐lactone slowly hydrolyzes in water to form gluconic acid.
14 22.9%.
15 50 ml.
3 Properties of Sugars
3.1 Learning Outcomes
After completing this exercise, students will be able to:
1 Draw structures of common reducing and nonreducing sugars.
2 Explain the difference between a hemiacetal and an acetal.
3 Distinguish between reducing and nonreducing sugars experimentally.
3.2 Introduction
Sugars are polyhydroxylated aldehydes or polyhydroxylated ketones (Figure 3.1). Thus, they participate in reactions characteristic of alcohols and aldehydes or ketones. Please review the sections in your organic chemistry textbook that describe reactions for alcohols, aldehydes, and ketones.
Recall that alcohols react reversibly with aldehydes or ketones to form hemiacetals or hemiketals. When the alcohol and carbonyl groups are on the same molecule, as is the case with sugars, a cyclic or ring structure is formed (Figure 3.2).
Note that hemiacetals contain a carbon atom bonded to an –OH group and an –O–R group. Hemiacetals are relatively unstable. In aqueous solution, the open and closed ring forms are both present in equilibrium. Thus, sugars like glucose participate in reactions characteristic of aldehydes even though the predominant form is the hemiacetal.
Sugars containing the hemiacetal group are called reducing sugars because they are capable of reducing various oxidizing agents. Several well‐known assays, based on this tendency to oxidize, have been developed for detecting reducing sugars. These include the Tollen's test (sugars are mixed with Ag+ in aqueous ammonia solution), the Fehling's test (sugars are mixed with Cu2+ in aqueous tartrate solution), and the Benedict's test (sugars are mixed with Cu2+ in aqueous citrate solution). When mixed with these solutions, reducing sugars are oxidized causing a reduction in the valence of the metal ion. In the Tollen's test, a shiny mirror of elemental silver (Ag0) forms on the inside surface of the test tube. In the Fehling's and Benedict's tests, Cu2+ is reduced to Cu1+ which reacts with water to form reddish brown cuprous oxide. Benedict's reagent is used in some of the “sugar sticks” diabetics use to test their urine for spilled sugar. The following chemical equation describes the Benedict’s test [1]:
Figure 3.1 Three representations of the structure of glucose, a polyhydroxylated aldehyde.
Figure 3.2 Balanced equation showing the nucleophilic attack of the C‐5 hydroxyl oxygen of glucose on the carbonyl carbon of the same molecule to form a hemiacetal.
When conditions are right, hemiacetals can react with alcohols to form acetals. For example, glucose in the hemiacetal form might react with fructose to form the acetal better known as sucrose (