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Properties of Water
A. The Water Molecule
1. Polarity: the charge on water is unevenly distributed. So the H’s are partially (+) and the O is partially (-)
2. Hydrogen Bonding: the partial (+) on the H’s is attracted to the partial (-) on other O’s
a. H2 behaves this way with O2, N2, and F2
b. H-bonds are not as strong as ionic or covalent but give water unique characteristics
* Cohesion: the attraction between molecules of the same substance (water to water)
* Adhesion: the attraction between molecules of different substances (water to glass)
* Heat Capacity: the amount of energy to raise the temperature of a substance
- in the case of H2O, H-bonds give it a high heat capacity making water a good cooling substance
B. Solutions and Suspensions
1. A mixture is a material composed of two or more elements or compounds that are mixed together but not
chemically combined.
a. Think of mixing sugar and sand. Each grain of sugar still has the properties of sugar; sand of sand
2. Solutions: mixtures where all components are equally distributed
a. solute: that which is dissolved
b. Solvent: that which does the dissolving
c. Water is known as the universal solvent because it can dissolve ionic compounds and polar molecules
3. Suspensions: mixture of water and non-dissolved material
a. Blood is a mix of water and dissolved compounds (solution)
* but there are also undissolved particles that stay suspended (暫停) in the blood (suspension)
C. Acids, Bases, and pH
1. Self ionization of water: water actually exists in an equilibrium state
a. H2O
H+ + OHb. This occurs in 1 molecule in 550 million
c. The positive = the negative so pure water is neutral
2. The pH Scale: indicates the concentration of H+ or [H+]
a. ranges from 0-14
b. 7 = neurtral, lower than 7 = acidic, higher than 7 = basic
3. Acids: any compound that forms H+ ions in solution (have a higher [H +])
a. stronger acids have pH = 1-3
4. Bases: compound that produces hydroxide ions (OH-)
a. also called alkaline solutions have lower [H+] that pure water
b. have pH ranging from 11-14
5. Buffers: weak acids or bases that can react with strong acids or bases to prevent big pH changes.
a. play an important role in maintaining homeostasis in organisms.
*you can eat acidic things without poisoning your blood with acids.
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