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Meera Hodges

Meera Hodges . 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;

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Meera Hodges

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  1. Meera Hodges Water

  2. 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.

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

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

  5. Hydrogen 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)

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

  7. Polar Molecules • 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.

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

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

  10. Non-Polar Covalent Bonds • 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

  11. Polarity of water • 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!

  12.  discuss the differences between hard and soft water;

  13. Hard 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

  14. Hard Water • 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

  15. 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

  16. Effects of Hard Water • 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!

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

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

  19. 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.

  20. (D)  compare the heat of fusion and the heat of vaporization;

  21. http://www.adaptivecurriculum.com/proxy/AC/TPlayer/v0.0.9/actplayer.jsp#http://www.adaptivecurriculum.com/proxy/AC/TPlayer/v0.0.9/actplayer.jsp#

  22. Latent Heat • 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

  23. Heat of Fusion • 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.

  24. Heat of Vaporization • 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!

  25. Boiling Point • 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 1000C.

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

  27. http://www.youtube.com/watch?v=2k5s7dBQhbc&feature=related • http://www.youtube.com/watch?v=3F_50xt0WLc&feature=related

  28. Functions of water in the body • 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

  29.  explain the functions of water in food preparation

  30. Functions of water in food preparation • The four main functions of water in food preparation are: • Water content in food • Water in heat transfer • Water as a solvent • Water as a dispersing medium

  31. Water content in food • 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

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

  33. Water in heat transfer • 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.

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

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