presentation notes - water - the essential molecule for...

Presentation Notes Water – The Essential Molecule for Life!

Water - The Essential Molecule for Life! Copyright © Texas Education Agency, 2015. All rights reserved.

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Food Science

Water – The Essential Molecule for Life!



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CopyrightCopyright © Texas Education Agency, 2015. 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:

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Copyright © Texas Education Agency, 2015. All rights reserved. 2



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H2O

3Copyright © Texas Education Agency, 2015. All rights reserved.

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.



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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


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.



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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


Covalent bond - a chemical bond formed between atoms

by the sharing of electron.



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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


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.



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Hard vs. Soft WaterHard 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


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?



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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

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.



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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


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



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Water in Food Preparation


Water is a main ingredient in many foods.



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Functions

• Necessary for forming food mixtures

• Transfers heat


Water serves these two main functions in preparing food

products.



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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


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.



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Heat Transfers

• Leavening agent

• Steam cooking

– More flavorful

– More nutritious


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.



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Water in the Body


Water is needed for many body functions.



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Functions

1. Maintains body temperature

2. Transports nutrients

3. Serves as a reactant in metabolism

4. Becomes part of body tissue


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.



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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


It is important to stay hydrated as we can live much longer

without food but not without water.

Do you drink lots of water?



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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.


Are you thirsty?

Remember to drink water throughout the day before you

become thirsty.



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Lack of Water

Can:

• Begin to damage body tissue

• Lower energy levels

• Reduce coordination


Water is a basic nutrient and often overlooked but it is vital

to your health.



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The Properties of Water


(click on link)

(image from video)

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.

https://www.youtube.com/watch?v=aVmU3CLxvgU



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Slide 20


What does this quote mean to you?



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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?


Answers to the questions are found within the slide

presentation or may vary with class discussion.



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Questions?



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References and ResourcesImages:

• 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)

http://water.epa.gov/learn/kids/drinkingwater/teachers_9-12.cfm

• Science Buddies Staff. (2015, March 20).

Chemistry of Ice-Cream Making: Lowering the Freezing Point of Water.

Retrieved May 21, 2015 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p013.shtml

• Science Buddies Staff. (2014, October 3).

Investigating the 'Mpemba Effect': Can Hot Water Freeze Faster than Cold Water?

Retrieved May 21, 2015 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p032.shtml

• Science Buddies Staff. (2014, October 6).

Saturated Solutions: Measuring Solubility.

Retrieved May 21, 2015 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p050.shtml

• Science Buddies Staff. (2014, November 18).

Electrolyte Challenge: Orange Juice Vs. Sports Drink.

Retrieved May 21, 2015 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p053.shtml

Copyright © Texas Education Agency, 2015. All rights reserved. 23



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Websites:

• The USGS Water Science School

Water Properties - Facts and Figures About Water

http://water.usgs.gov/edu/water-facts.html

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.

https://www.youtube.com/watch?v=aVmU3CLxvgU

References and Resources

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