What do you think are some useful characteristics of water? How do you think water helps the body function?

HOMEWORK In 5 sentences, Explain why water is so important in biology. (Hint: explain using the properties of water)

Chemistry of Water

1. Water molecules form by COVALENT BONDS between two hydrogen (H) atoms and one oxygen (O) atom. A. Water’s Polarity

a. Water molecules are POLAR - one side of the molecule is positively charged, while the other is negative.

- Oxygen is negative, hydrogen is positive.

b. Opposite charges are attracted to each other b. Opposite charges are attracted to each other. - HYDROGEN BONDS form between H of one water molecule and O of another.

High Specific Heat Water has a high specific heat because of Hydrogen bonds** Specific Heat: How much heat energy it takes to raise the temperature by 1 degree.

1. HYDROGEN BONDS allow water to have some unique properties. a 1. HYDROGEN BONDS allow water to have some unique properties. a. COHESION – water molecules HYDROGEN BOND to other water molecules. B. Properties of Water

- COHESION creates SURFACE TENSION, or solid-like behavior on the surface of water. Ex: Something light can “sit” on the surface of water.

b. ADHESION – water molecules hydrogen bond to molecules of other surfaces. Ex: Water drops remain in an “empty” water bottle.

CAPILLARY ACTION The ability of a liquid to flow through narrow spaces without being affected by gravity or other natural forces. Combination of adhesion and cohesion help this happen.

Review

1. MIXTURE - combination of two or more substances where each substance retains its individual properties. C. Mixtures with Water

2. MIXTURES can be either HOMOGENEOUS or HETEROGENEOUS.

a. HOMOGENEOUS MIXTURES are evenly distributed throughout a. HOMOGENEOUS MIXTURES are evenly distributed throughout. They are also known as SOLUTIONS.

-In a SOLUTION, the SOLVENT is the liquid into which something is dissolved. -The SOLUTE is what is being dissolved in the SOLVENT.

b. If something dissolves in water, it is SOLUBLE b. If something dissolves in water, it is SOLUBLE. -Only other POLAR substances dissolve in water.

3. Water is known as the “universal SOLVENT” because it will dissolve many SOLUTES. a. This is due to water’s POLARITY.

b. ACIDS - substances that release H+ when dissolved in water b. ACIDS - substances that release H+ when dissolved in water. -More H+ = more ACIDIC.

c. BASES - substances that release hydroxide ions (OH−) when dissolved in water. -More OH- = more BASIC.

4. Amount of H+ or OH- ions in a solution determines the strength of an ACID or BASE a. The amount of of H+ in a solution is called pH.

-ACIDS have pH values < 7; BASES have pH values > 7

5. Metabolic processes require a neutral pH (6. 5-7. 5). a 5. Metabolic processes require a neutral pH (6.5-7.5). a. BUFFERS - mixtures that balance the pH of an substance. -Ex: BUFFERS in our blood keep the pH at 7.4.