Water

• The student explains the properties of water. The student is expected to:
• (A) identify the properties of water that make it a polar molecule;
• (B) describe hydrogen bonds and how they differ from covalent bonds;
• (C) discuss the differences between hard and soft water;
• (D) compare the heat of fusion and the heat of vaporization;
• (E) explain the functions of water in food preparation; and
• (F) identify the functions of water in the body.

• (A) identify the properties of water that make it a polar molecule;

• (B) describe hydrogen bonds and how they differ from covalent bonds;

• Hydrogen bond – is an attractive force between any molecules in which hydrogen is covalently bonded to a highly electronegative element usually (N, O, F)

• Covalent bond – the sharing of electrons to become stable
• Usually occurs between two non-metals
• Creates a molecule

• Polar molecules - have a partial negative charge on one end, and the other side has a partial positive charge. (dipole)
• Since the Oxygen has the electrons around it for most of the time, it has a slight negative charge.
• The Hydrogen loses out meaning that the
Hydrogen carries a slight positive charge.
•The little squiggle is a sigma and means slightly.

Polar molecules are pulled toward each other, like magnets, with opposite charges attracting.

•are typically asymmetrical
(lone pairs of electrons)
•Polar molecules are soluble (can be dissolved) in polar substances
LIKE DISSOLVES LIKE

• Non-polar molecules are usually symmetrical, so charges are balanced.
• Non-polar molecules are soluble in non-polar substances
• If two substances share the same polarity they will dissolve
• LIKE DISSOLVES LIKE

• Electronegativity – the measure of how strongly an atom attracts electrons in a chemical bond
• The oxygen end of the water molecule is somewhat negative
• The hydrogen end is somewhat positive
• This makes water a polar molecule because it has a positive end and a negative end!

• discuss the differences between hard and soft water;

• Hard water- contains calcium and magnesium ions
• Evidence of hard water
– cooking dried peas and beans such as lentils takes longer
– Soap does not dissolve as effectively as compared to soft water
– Laundry washed in hard water leaves a grayish film
– Dishes often have water spots

• Hardness refers to the presence of calcium and magnesium ions in water
(and sometimes iron).
• Ions come from dissolved rock the water has passed through.
• Affects properties of tap water

– cooking dried peas and beans such as lentils takes longer
– Soap does not dissolve as effectively as compared to soft water
– Laundry washed in hard water leaves a grayish film
– Dishes often have water spots

• Calcium and iron deposits can build up in appliances and on faucets:
– Washing machine
– Dish washer
– Steam iron
• Shortens their life span and adds to landfill problem!

• Water with very low concentrations of minerals.
• Soap lathers easily and is sometimes difficult to rinse off.

• Water that has been purified through evaporation and condensation so remove minerals such as calcium.
• Is distilled water soft water?

Class Discussion about Waco Water a dissolved calcium and magnesium concentration at or above
120 mg per liter is considered hard water
However, many people find that a concentration of only 85 mg per liter still creates some of the problems associated with hard water.

• (D) compare the heat of fusion and the heat of vaporization;

• http://www.adaptivecurriculum.com/proxy/A
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• Latent heat – the amount of heat required to create a phase change without a change in temperature
– Two types of latent heat
• Latent heat of fusion
• Latent heat of vaporization

• Heat of fusion – the amount of heat required to change 1.0 g of a substance from a solid to a liquid phase
• Example: Water has a heat of fusion of
80cal/g.
• It takes 80 calories of heat to change 1 gram of water from a solid to liquid.

• Heat of vaporization – the amount of heat needed to change 1.0 g of a substance from a liquid phase to a gas phase
• Example: Water has a heat of vaporization of
540 cal/g
• It takes 540 calories to change one gram of water from liquid to steam!

• Boiling point of a liquid – the temperature at which its vapor pressure equals the air pressure above it
• Example at normal atmospheric pressure, water boils at 100 0 C.

• (F) identify the functions of water in the body.

• http://www.youtube.com/watch?v=2k5s7dBQ hbc&feature=related
• http://www.youtube.com/watch?v=3F_50xt0
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• 50 -65% of your weight is water
• The body obtains water from two sources: food and liquid consumed
• You need to drink 6-8 glasses of water each day
• Water helps maintain constant body temperature

• explain the functions of water in food preparation

• The four main functions of water in food preparation are:
1. Water content in food
2. Water in heat transfer
3. Water as a solvent
4. Water as a dispersing medium

• Free water- water that is readily separated from food that are sliced, diced or dried.
– Example: bread getting crisp in the toaster as the heat evaporates the free water

• Bound water – water that cannot be easily separated in food
Example : Foods where the water molecule is bonded tightly and the water cannot escape

• Water transfers and moderates the effects of heat.
• A potato heated by itself in a pan will burn but surrounding that same potato with water ensures that the heat will be evenly distributed.
• Water also transfers heat more efficiently, which explains why a potato heats faster in boiling water than in the oven.
• Because water has a higher specific heat than other substances, it buffers changes in temperature. More energy is needed to increase the temperature of 1 gram of water than 1 gram of fat. For example, the specific heat of oil is 0.5; thus it heats twice as fast as water when given the same amount of heat.

• Solvent – the substance that is dissolving another substance
• Solute- the substance that is dissolved
• Water is commonly referred to as the universal solvent