Water The Essential Molecule for Life!

Transcription

1 Slide 1 Water The Essential Molecule for Life! Food Science Page1

2 Slide 2 Copyright Copyright Texas Education Agency, These Materials are copyrighted and trademarked as the property of the Texas Education Agency (TEA) and may not be reproduced without the express written permission of TEA, except under the following conditions: 1) Texas public school districts, charter schools, and Education Service Centers may reproduce and use copies of the Materials and Related Materials for the districts and schools educational use without obtaining permission from TEA. 2) Residents of the state of Texas may reproduce and use copies of the Materials and Related Materials for individual personal use only, without obtaining written permission of TEA. 3) Any portion reproduced must be reproduced in its entirety and remain unedited, unaltered and unchanged in any way. 4) No monetary charge can be made for the reproduced materials or any document containing them; however, a reasonable charge to cover only the cost of reproduction and distribution may be charged. Private entities or persons located in Texas that are not Texas public school districts, Texas Education Service Centers, or Texas charter schools or any entity, whether public or private, educational or non-educational, located outside the state of Texas MUST obtain written approval from TEA and will be required to enter into a license agreement that may involve the payment of a licensing fee or a royalty. For information contact: Office of Copyrights, Trademarks, License Agreements, and Royalties, Texas Education Agency, 1701 N. Congress Ave., Austin, TX ; phone ; copyrights@tea.state.tx.us. 2 Page2

3 Slide 3 H2O 3 The clear liquid that has no color, taste or smell. It falls from clouds as rain, forms streams, lakes and seas. Is used for drinking, washing and more. Three percent of the earth s surface is fresh water. Page3

4 Slide 4 Properties of Water 1. A chemical compound of one oxygen an two hydrogen atoms 2. Small compound held together by covalent bonds 3. Hydrogen is slightly positive and oxygen is slightly negative 4. Commonly referred to as H2O 4 Water has a: greater ability to conduct energy higher boiling and melting points lower density more surface tension The water molecule is highly cohesive it is very sticky. Water is the most cohesive among the non-metallic liquids. Page4

5 Slide 5 Covalent Bonds Oxygen and hydrogen share electrons Hydrogen is slightly positive Oxygen is slightly negative Oxygen is more electronegative than hydrogen This makes water a polar molecule Opposite electrical charges 5 Covalent bond - a chemical bond formed between atoms by the sharing of electron. Page5

6 Slide 6 Hydrogen Bonds Bonds between molecules are much weaker But stronger than any force between nonpolar molecules Water is a polar molecule so the hydrogen bonds are strong 6 Hydrogen bond - an electrostatic attraction between a hydrogen atom in one polar molecule (as of water) and a small electronegative atom (as of oxygen, nitrogen, or fluorine) in usually another molecule of the same or a different polar substance Not all polar molecules have hydrogen bonds. Page6

7 Slide 7 Hard vs. Soft Water Hard Water Contains calcium or magnesium ions Can affect the quality of food prepared in it Dishes washed in a dishwasher may have water spots Does not dissolve soap as effectively Interferes with water s tenderizing effect Laundry tends to have a grayish film Soft Water Does not contain calcium or magnesium Water with bicarbonate ions may be softened by boiling it Water with sulfates must pass through an ion exchange filter to remove calcium or magnesium ions Water softener appliances may be used in hard water areas 7 Calcium and magnesium often dissolve in water as it passes through the ground Dried beans, lentils and peas have to cook longer in hard water. Iced tea may turn cloudy. Do you have a water softener in your home? Page7

8 Slide 8 Heat of Fusion To melt ice, heat is required 80 calories of heat energy is needed to change 1.0 gram of water from solid to liquid 80 calories of heat energy are released for every 1.0 grams of liquid water that freezes 8 Heat of fusion - heat required to melt a solid; specifically, the amount required to melt unit mass of a substance at standard pressure. Less energy is needed to break the hydrogen bonds. Water freezes at 32 F and boils at 212 F. Water is unusual in that the solid form, ice, is less dense than the liquid form, which is why ice floats. Page8

9 Slide 9 Heat of Vaporization To boil water, more energy is needed to break ALL of the hydrogen bonds 540 calories per gram to change 1.0 gram of water from liquid to steam The gas turns to steam and can be more dangerous than boiling water 9 Heat of vaporization - heat absorbed when a liquid vaporizes; specifically, the quantity of heat required at a specified temperature to convert unit mass of liquid into vapor. Water is unique in that it is the only natural substance that is found in all three physical states liquid, solid and gas at the temperatures normally found on Earth. Steam burns from cooking occur when the steam condenses on to the skin, releasing its heat of condensation (reverse of heat of vaporization). Why does it take more energy to vaporize than to melt ice? Answer More energy is needed to break all the hydrogen bonds Page9

10 Slide 10 Water in Food Preparation 10 Water is a main ingredient in many foods. Page10

11 Slide 11 Functions Necessary for forming food mixtures Transfers heat 11 Water serves these two main functions in preparing food products. Page11

12 Slide 12 Food Mixtures Gases, liquids and solids can be found in water solutions Examples: Gases carbonated beverages Liquids vinegar for pickled foods Solids salt and sugar; tea and coffee 12 Water is called the "universal solvent" because it dissolves more substances than any other liquid. When preparing foods with water, knowing how water works in the mixtures will be useful. Page12

13 Slide 13 Heat Transfers Leavening agent Steam cooking More flavorful More nutritious 13 As water expands in doughs that are heated, it becomes a gas that needs more space. What food is an example of using steam as a leavening agent? Popovers! Much of the flavor and nutrients of foods remain in steamed foods compared to boiling foods where flavor and nutrients are lost in the water. Page13

14 Slide 14 Water in the Body 14 Water is needed for many body functions. Page14

15 Slide 15 Functions 1. Maintains body temperature 2. Transports nutrients 3. Serves as a reactant in metabolism 4. Becomes part of body tissue 15 When body temperature rises, you perspire. Water needs energy to evaporate and pull the heat away from the body. Minerals and water-soluble vitamins must dissolve in water before be transported to where they are needed. Water also helps transport waste products out of the body. Metabolism is the combination of chemical and physical processes that react to produce, transfer and store energy to make new cells. The body is composed of about 60% water and becomes part of the body tissue. Page15

16 Slide 16 Hydration Most people need six to eight glasses of water a day The body gets the water it needs from: Beverages Foods you eat Water has no calories 16 It is important to stay hydrated as we can live much longer without food but not without water. Do you drink lots of water? Page16

17 Slide 17 Thirst A feeling that lets your body know it needs water By that time, your water supply is already low. Consume water throughout the day before you become thirsty. 17 Are you thirsty? Remember to drink water throughout the day before you become thirsty. Page17

18 Slide 18 Lack of Water Can: Begin to damage body tissue Lower energy levels Reduce coordination 18 Water is a basic nutrient and often overlooked but it is vital to your health. Page18

19 Slide 19 The Properties of Water (click on link) (image from video) 19 Click on the hyperlink to view the video: The Properties of Water This four minute animation describes the properties of water that support life. These properties include solvency, cohesion and adhesion, high surface temperature, high heat capacity, high heat of vaporization and varying density. Page19

20 Slide What does this quote mean to you? Page20

21 Slide 21 Let s Review! 1. How much of the earth s surface is water? 2. What is a covalent bond? What is a hydrogen bond? 3. What is the difference between hard and soft water? 4. What is an example of heat fusion? Heat vaporization? 5. How many calories does water have? 6. How is water used in food? 7. What are the four functions of water in the body? 8. How can you tell when you are thirsty? 21 Answers to the questions are found within the slide presentation or may vary with class discussion. Page21

22 Slide Questions? Page22

23 Slide 23 References and Resources Images: Shutterstock images. Photos obtained with subscription. (Slides 1, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21) Textbooks: Mehas, K. Y. & Rodgers, S. L. (2002). Food science: The biochemistry of food and nutrition. New York, NY: Glencoe/McGraw-Hill. Ward, J. D. & Ward, L. T. (2015). Principles of food science. Tinley Park, IL: Goodheart-Willcox Company. Websites: Environmental Protection Agency Water: Drinking Water - For Teachers (Grades 9-12) Science Buddies Staff. (2015, March 20). Chemistry of Ice-Cream Making: Lowering the Freezing Point of Water. Retrieved May 21, 2015 from Science Buddies Staff. (2014, October 3). Investigating the 'Mpemba Effect': Can Hot Water Freeze Faster than Cold Water? Retrieved May 21, 2015 from Science Buddies Staff. (2014, October 6). Saturated Solutions: Measuring Solubility. Retrieved May 21, 2015 from Science Buddies Staff. (2014, November 18). Electrolyte Challenge: Orange Juice Vs. Sports Drink. Retrieved May 21, 2015 from 23 Page23

24 Slide 24 References and Resources Websites: The USGS Water Science School Water Properties - Facts and Figures About Water YouTube : The Properties of Water This four minute animation describes the properties of water that support life. These properties include solvency, cohesion and adhesion, high surface temperature, high heat capacity, high heat of vaporization and varying density Page24