Principles of Food Science 5e, Textbook Page 94 (112 of 608)

94 Principles of Food Science An oxygen atom has two empty spaces in its outer shell. The hydrogen atom remaining in the OH group shares its electron with the oxygen atom. The transfer of the electron from the hydrogen atom that broke away fills the oxygen atom’s outer electron shell. This means the OH group has a total of 10 electrons. However, it has only nine protons, eight in the oxygen atom and one in the hydrogen atom. Therefore, the OH group becomes a negatively charged hydroxide ion, which is represented by the symbol OH–. See 6-2. Hydrogen, hydronium, and hydroxide ions are used to define acids and bases. Acids are substances that produce hydrogen or hydronium ions in water- based solutions. Acids have a positive charge. Bases are substances that produce hydroxide ions in water- based solutions. Bases have a negative charge. Bases are also called alkalis. If acids and bases combine to form a compound with ionic bonds, that compound is called a salt. A substance is neutral when it has an equal number of positive and negative charges. Pure water is neutral because it always has an equal number of hydronium and hydroxide ions. Theories of Acids and Bases In 1923, two scientists independently developed a theory that explained how acids and bases work at the molecular level. The scientists who developed this theory were the Danish chemist Johannes Bronsted and the English chemist Thomas Lowry. These chemists found that acids and bases separate in water to form ions. In chemical reactions, acids donate hydrogen ions (H+) and bases accept hydrogen ions. Because a hydrogen atom has only one electron to give up, a hydrogen ion is a single proton. Therefore, acids are compounds that easily give up the proton from a hydrogen atom. They are proton donors. Acids have The Ionization of Water + + – – +1 Water molecule (H 2 O) Water molecule (H2O) Water molecule (H 2 O) Hydrogen ion (H+) Hydronium ion (H3O+) Hydroxide ion (OH–) Hydroxide ion (OH–) +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +8 +8 +8 +8 +8 +8 Goodheart-Willcox Publisher 6-2 When a hydrogen atom breaks away from a water molecule, the atom leaves its electron behind. This creates a positive hydrogen ion and a negative hydroxide ion. The hydrogen ion is immediately drawn to another water molecule, creating a hydronium ion. Copyright Goodheart-Willcox Co., Inc.

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94 Principles of Food Science An oxygen atom has two empty spaces in its outer shell. The hydrogen atom remaining in the OH group shares its electron with the oxygen atom. The transfer of the electron from the hydrogen atom that broke away fills the oxygen atom’s outer electron shell. This means the OH group has a total of 10 electrons. However, it has only nine protons, eight in the oxygen atom and one in the hydrogen atom. Therefore, the OH group becomes a negatively charged hydroxide ion, which is represented by the symbol OH–. See 6-2. Hydrogen, hydronium, and hydroxide ions are used to define acids and bases. Acids are substances that produce hydrogen or hydronium ions in water- based solutions. Acids have a positive charge. Bases are substances that produce hydroxide ions in water- based solutions. Bases have a negative charge. Bases are also called alkalis. If acids and bases combine to form a compound with ionic bonds, that compound is called a salt. A substance is neutral when it has an equal number of positive and negative charges. Pure water is neutral because it always has an equal number of hydronium and hydroxide ions. Theories of Acids and Bases In 1923, two scientists independently developed a theory that explained how acids and bases work at the molecular level. The scientists who developed this theory were the Danish chemist Johannes Bronsted and the English chemist Thomas Lowry. These chemists found that acids and bases separate in water to form ions. In chemical reactions, acids donate hydrogen ions (H+) and bases accept hydrogen ions. Because a hydrogen atom has only one electron to give up, a hydrogen ion is a single proton. Therefore, acids are compounds that easily give up the proton from a hydrogen atom. They are proton donors. Acids have The Ionization of Water + + – – +1 Water molecule (H 2 O) Water molecule (H2O) Water molecule (H 2 O) Hydrogen ion (H+) Hydronium ion (H3O+) Hydroxide ion (OH–) Hydroxide ion (OH–) +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +8 +8 +8 +8 +8 +8 Goodheart-Willcox Publisher 6-2 When a hydrogen atom breaks away from a water molecule, the atom leaves its electron behind. This creates a positive hydrogen ion and a negative hydroxide ion. The hydrogen ion is immediately drawn to another water molecule, creating a hydronium ion. Copyright Goodheart-Willcox Co., Inc.

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Chapter 6 Ions: Charged Particles in Solution 95 extra H+ ions they can contribute. Bases easily accept protons and are therefore called proton acceptors. Bases have a negative charge and will readily accept H+ ions. These facts about the nature of acids and bases are summarized in the Bronsted-Lowry theory. This theory states that acids are proton donors and bases are proton acceptors. This scientific explanation also states that, whenever possible, acids and bases natu- rally react with their opposites to achieve a neutral charge. The Bronsted-Lowry theory defines acids and bases in terms of proton needs that will achieve this balance. The Bronsted-Lowry theory is the most compre- hensive theory about the nature of acids and bases. Even so, it does not explain the reaction of carbon dioxide (CO2) in water-based mixtures like soft drinks and egg whites. Carbon dioxide is the source of carbonation for soft drinks. However, it does not have a hydrogen ion or proton to donate. Another discovery about acids and bases was made in 1923 by an American chemist named Gilbert Newton Lewis. Lewis discovered that acid/base reactions could be described in terms of the move- ment of electrons. In acids and bases where there is no hydrogen involved, ions are looking to donate or accept electrons. Substances that donate electrons are bases, and substances that accept electrons are acids. Carbon dioxide increases the acidity of a mixture because, in the presence of water, it is an electron acceptor. Identifying Acids and Bases You can identify acids and bases in two common ways. One way is through sensory evaluation. You can also identify acids and bases with the use of organic dyes. Sensory Evaluation of Acids and Bases A simple way to identify many acids and bases is by sensory evaluation, such as taste testing. You must use caution, however, because not all acids and bases are safe to taste. Poisoning and burning can result from tasting certain acids and bases. In those cases where testing can be done safely, you would find that acids taste sour. Lemons, grapefruit, cranberries, vinegar, and yogurt contain acids that are safe to taste, 6-3. Bases have a bitter flavor. Quinine water, milk of magnesia, and baking soda are examples of bases that are safe to taste. Another type of sensory evaluation that can help you identify bases is to touch them with your fingers. Again, you must use caution. Some bases can cause problem that may be tied to excess sodium intake is stomach cancer. Sodium appears to irritate the lining of the stomach, which increases the chances of cancer cells developing. Excess sodium has an additional risk for athletes. Too much salt causes dehydration of cells and increases potassium loss, which leads to chronic fatigue. To reduce your risk of these health concerns, registered dietitians recommend that you avoid high- sodium foods. Foods highest in sodium are processed foods, especially mixes, frozen entrees, and canned foods. Read labels, cook from scratch, limit “instant” products, and select low-sodium and no-salt options. Try flavoring foods with pepper, fresh herbs, onion, garlic, and spices that are all low in sodium and high in flavor. Taste before reaching for the salt shaker. Keep in mind that it may take about four to six weeks to become used to foods with less salt. Nutrition News Salt in the Diet The 2015 Dietary Guidelines for Americans recommend a maximum sodium intake of 2,300 mg for most people. The average American 19 to 51 years of age consumes around 3,400 mg of sodium per day. Higher levels of sodium may be needed by athletes after high-intensity activity and by those who sweat excessively. People with high blood pressure, diabetes, or chronic kidney disease may need to keep salt consumption below 1,500 mg per day. There is some evidence that salt preference is established through exposure between the ages of one and three. Limiting sodium in the diets of young children may help them control their salt intake when they grow older. Research has linked excess sodium in the diet to a number of health problems. For some people, excess sodium can increase the risk of high blood pressure. Sodium also speeds calcium loss from bones. For each teaspoon of salt you consume in a day, you will lose 23 mg of calcium from your bones. This equals 10% of your total bone mass over each 10-year period. Bone loss is associated with fractures and related complications, especially in later life. A third health Copyright Goodheart-Willcox Co., Inc.

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93 Y ou have probably heard the terms sour stomach, bitter herbs, buffered aspirin, heartburn, and acid rain. What do these terms describe? How are they related? To answer these questions, you need to take a close look at charged particles in solutions. You also need to define the terms acids, bases, and salts. Acids, bases, and salts are a related group of compounds. The structure and function of these compounds could not be defined until the nineteenth and early twentieth centuries. However, these substances have been recognized as a fundamental category of chemical compounds since ancient times. These substances have been primary factors in food pres- ervation and wine, cheese, and bread making throughout history, 6-1. Acids and bases also play a key role in digestion and many other bodily functions. Understanding how this classification of compounds func- tions can improve your baking skills. Knowledge about acids, bases, and salts can also help you maintain a safer, healthier food supply. Defining Acids and Bases Ions are charged particles or particles that have an imbalance of electrons and protons. Ions of opposite charges can form ionic bonds. These concepts provide a basis for learning about acids and bases and how they react in foods. Looking at water molecules can also help you better understand acids, bases, and salts. The Ionization of Water You will recall that the chemical formula for water is H2O. Two hydrogen atoms are bonded to one oxygen atom. However, a close analysis of water shows that pure water is not just a group of H2O molecules. At any given time, a small number of molecules in a volume of water are separating into ions and then recombining. This process of forming ions is called ionization. It is represented by the chemical equation below. The ability of the reaction to move in either direction is represented by a double-ended arrow. H2O H+ + OH– During the ionization process, a hydrogen atom breaks away from the water molecule. It leaves its electron with the oxygen atom. Remember that atoms prefer to have their outermost electron shell either full or empty. When the hydrogen atom gives its only electron to the OH group, it has an empty electron shell. The hydrogen atom becomes a positively charged hydrogen ion, which is represented by the symbol H+. However, scientists have found that hydrogen ions do not exist in water. A hydrogen ion has no electrons. Therefore, it is immediately drawn to bond with a water molecule with which it can share a pair of electrons. This forms a group of three hydrogen atoms and one oxygen atom. The group has a total of 11 protons but only 10 electrons, giving the group a positive charge. A hydrogen atom bonded to a water molecule is called a hydronium ion and is represented by the symbol H3O+. Key Terms ionization hydrogen ion hydronium ion hydroxide ion acid base salt neutral proton donor proton acceptor Bronsted-Lowry theory organic dye pH scale indicator titration endpoint equivalence point neutralization concentration Avogadro’s number mole molarity (M) chyme buffer botulism chemical leavening agent Goodshoot/Getty Images Plus 6-1 The production of these food products is based on principles of acid and base reactions. Copyright Goodheart-Willcox Co., Inc.

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Page 2Unit 1 The Science of Food click to expand contents

Page 56Unit 2 Basic Chemistry click to expand contents

Page 132Unit 3 Organic Chemistry: The Macronutrients click to expand contents

Page 238Unit 4 Food Chemistry: The Microcomponents click to expand contents

Page 324Unit 5 Food Microbiology: Living Organisms in Food click to expand contents

Page 394Unit 6 Food Preservation and Packaging click to expand contents

Page 464Unit 7 Working with Complex Food Systems click to expand contents

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