Water – The Essential
Molecule for Life!
Food Science
Copyright
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H2O
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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
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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
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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
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Hard vs. Soft Water
Hard Water
Soft Water
Contains calcium or magnesium ions
Does not contain calcium or
magnesium
• Can affect the quality of food
prepared in it
• Dishes washed in a dishwasher may
have water spots
• Water with bicarbonate ions may
be softened by boiling it
• Does not dissolve soap as
effectively
• Water with sulfates must pass
through an ion exchange filter to
remove calcium or magnesium ions
• Interferes with water’s tenderizing
effect
• Water softener appliances may be
used in hard water areas
• Laundry tends to have a grayish film
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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
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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
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Water in Food Preparation
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Functions
• Necessary for forming food
mixtures
• Transfers heat
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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
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Heat Transfers
• Leavening agent
• Steam cooking
– More flavorful
– More nutritious
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Water in the Body
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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
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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
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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.
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Lack of Water
Can:
• Begin to damage body tissue
• Lower energy levels
• Reduce coordination
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The Properties of Water
(click on link)
(image from video)
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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?
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Copyright © Texas Education Agency, 2015. All rights reserved.
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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)
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.
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References and Resources
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
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