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Water: The Universal SolventChapter 7
Water is the only substance in nature found in abundance in solid, liquid, and gas state.
Water is the main component in many foods-
Water is a nutrient
Nutrients are ______________________________.
Water
Chemically composed of one oxygen atom and two hydrogen atoms =
Covalent bonds Physical properties of the compound
Higher melting and boiling point More surface tension Lower density Greater ability to conduct energy
The Structure of Water
Nonpolar covalent bond- electrically neutral because the electrons are shared ___________.
Polar covalent bond- ________sharing of electrons within the molecule.
Water molecule
Types of Covalent Bonds
Hydrogen bond- attraction of a _________hydrogen end of one water molecule to the _________ oxygen ends of other water molecules.
Hydrogen bonds are intermolecular, or ________ _____________.
Intermolecular bonds are weaker than the covalent bonds within the molecule. (ex. Holding hands)
In water, the hydrogen of one atom is attracted to the oxygen of another.
Hydrogen Bonds
Surface Tension- force between molecules at the outside edge of a substance.
Water has greater surface tension than most compounds
Glass full = convex Glass not full = concave Water is both cohesive (clings to itself) and
adhesive (clings to something else as well as itself)
The adhesion in water is stronger than cohesion.
Surface Tension
____________- Force of the weight of gases in the air pressing down on a surface.
As atmospheric pressure changes, so does the boiling point of water.
The higher the atmospheric pressure, the higher the boiling point.
When water reaches its boiling point (100C at sea level) it changes from a liquid to a gas.
Pressure, Temperature, and Phase Changes
Anything added to a completely pure substance in an ___________.
Hot water could contain more impurities than cold water
Not always unsafe Salt
Can change physical and chemical characteristics
Flavor ________ Boiling point Freezing point Hydrogen bonding
Impact of Impurities in Water
2 main functions
Medium for transferring heat Cooking pasta
Necessary ingredient for forming many food mixtures
Baked goods (acts as leavening agent)
Functions of Water in Food Preparation
2 Advantages: _____________ More nutritious
To produce steam, water molecules have to absorb more energy.
Will take slightly longer to cook with steam rather than boiling water, unless under pressure.
Boiling water and steam = same temperature.
Cooking With Steam
WATER! The following are all mixtures of substances
dissolved in water Beverages Candies Baked goods Soups Stews Casseroles Sauces
The Most Common Solvent
Ex. - Carbonated beverages Carbon dioxide
Ex. - Cold water _________
Hot water has less oxygen because when water is boiled the oxygen escapes into the atmosphere. This would leave the water with a flat taste.
Gas-in-Water Solutions
Alcoholic beverages
Vinegar in water (pickle juice)
Fruit concentrates
Liquid-in-Water Solutions
Sugar and salt solutions Two most common solids Cause water to freeze at lower temp. and boil
at higher Sugar is used in much higher concentrations
than salt Tea and Coffee
Dissolves flavor compounds Increasing the brewing time will increase the
strength of flavor Ideal brewing temp is just below boiling point _____________ create bitter aftertaste.
Solid-in-Water Solutions
Water is a major part of most foods. Water Activity (Aw): the measure of partial water
pressure over food. Supports enzyme activity. Water becomes part of the structure of food in 3
main ways Free water: can be easily separated from food
tissues. Ex: grapefruit juice, lemon juice
Bound water: tied to the structure of large molecules.
Fruits, meats, vegetables
Hydrate: any chemical compound that is loosely bound with water.
Caffeine molecule
Water Content in Foods
Water Content in Food
Broccoli (cooked), 91% water
Eggs (raw), 75% water
Cheese Pizza (baked), 45% water
Brownies, 10% water
Functions of Water in the Body
Maintaining your body temperature
sweat Transporting nutrients
Minerals and water-soluble vitamins dissolve in water before transported
Reactant in metabolism Metabolism: combination of
chemical and physical processes occurring within the cells of the body.
Becomes part of the body tissue Body is composed of 60% water
6-8 glasses of water per day. A person can live much longer without food than
without water, but why can people who never drink water survive?
All foods are made up of water. Many foods that are high in water are also high in
sugar and salt More healthful to drink plain water than other
beverages as a water source because water has no calories.
Even diet soft drinks are bad because they contain excess sugars and phosphorous which can keep the body from absorbing other nutrients.
Meeting Your Body’s Water Needs
It is best to consume water regularly throughout the day.
After drinking sweetened beverages, thirst will occur in about 30 minutes.
Ice water relieves thirst faster than warm water. Constricts the stomach, forces water into the
bloodstream faster.
The Role of Thirst
• Fun fact: More water evaporates from skin and breath in high altitudes, where atmospheric pressure is low. So, if you are flying in an airplane you will need more water than normal to keep you hydrated.
Water is the most valuable resource because all life depends on it.
Since water is recycled through collected rainwater, lakes and rivers, and underground water, We had to find a way to keep it safe and clean.
Used to have many problems: Typhoid caused by bacteria from feces in water The Mediterranean Sea is toxic to most life-
forms due to factory and human waste In the 70’s lake Erie was thought to be “dead”
because the toxic buildup was so bad.
A Safe Water Supply
Pollutant: Anything that makes a substance impure.
Pollutants include bacteria, protozoa, viruses, and organic waste
Large volumes of microbes can deplete the oxygen levels in lakes and rivers. Cause fish to suffocate
Typhoid and Cholera are water-borne diseases caused by bacteria spread from human and animal feces.
Biological Pollutants
Three kinds of chemical contaminants: Metal ions, acids, and toxic substances
Metal Ions Temporary water hardness: caused by calcium
and magnesium ions. Permanently hard: When sulfur and chloride
compounds combine with calcium and magnesium.
Water softener: gives up the sodium and hydrogen and collects the calcium and magnesium compounds.
Acids Change the pH of water Acid rain caused by carbon monoxide, carbon
dioxide, sulfur oxide, nitrogen oxide, and hydrochloric acid.
Can kill plan and animal life
Chemical Contaminants in Water
GarbageLitter
Animals and fish die from both toxins and swallowing plastics.
Physical Contaminants in Water
Water has different contaminants in different parts of the world.
Companies have established water standards.
Remove contaminants from water before adding soft drink syrups.
Water Contaminants in the Beverage Industry