Chapter 3: Water AP Biology

Water Cells are 70-95% water- it is the medium of most everything biological.

Polarity of water Two hydrogen atoms held to an oxygen atom by polar covalent bonds. Oxygen is much more electronegative than hydrogen causing the electrons to be closer to the oxygen. Oxygen will be slightly negative Hydrogen will be slightly positive

Polarity of water The hydrogen atoms are attracted to other oxygens and the oxygen are attracted to other hydrogens, causing water to stick to other molecules of water.

The Four Emergent Properties of Water

1) Cohesion Water sticking to itself. -Water molecules are constantly moving around (in liquid state) and because of hydrogen bonding they form/reform/break apart continually but overall they stick to each other.

Cohesion and Adhesion

Cohesion This is useful in plants: Water will travel up the plant because as water evaporates out of the leaves the water will be “sucked” out of the ground.

Adhesion Adhesion- Water molecules sticking to another substance- water sticks to the vessels inside of a plant, assisting in the movement up the plant *capillary action Animation

Penny test with Soapy and Tap water

2) Moderation of temperature Heat- the total amount of kinetic energy due to molecular motion in a body of matter. Temperature is the scale in how heat is measured. Heat will ALWAYS travel from warmer to cooler, until they are balanced. Calorie- the amount of heat required to raise the temperature of 1g of water by 1°C. (Kilocalorie- 1 kg of water by 1°C)

Water is a “heat bank”- it absorbs and releases large amounts of heat with a MINIMAL change to its own temperature.

Moderation of temperature Very high specific heat- the amount of heat that must be gained/lost for 1g to change 1°C - IE: requires a great input of energy to raise the temperature - IE: requires a great amount of energy to be lost to drop temp - Can be summed up by saying water is RESISTANT to change in temperature

Moderation of temperature Reason- The heat energy has to disrupt all the H bonds before the molecules can start moving at a faster rate. Importance- Stabilization of body and ocean temp Properties of Water animation

Evaporative cooling - Heat of vaporization- Quantity of heat a liquid must absorb for it to go from a liquid to gas state. *Must break H bonds. Warmest molecules leave the liquid state first, cooling the temperature. -IE: A human body sweating and the earth’s climate

Evaporative cooling

3) Insulation of bodies of water by floating ice 3) Insulation of bodies of water by floating ice *Density of water as a solid Each water molecule will bond to four partners in ice form- forms a lattice. Ice is 10% LESS dense than water at 4°C. Once we go above 4°C the molecules will begin to spread out again.

*Water is MOST DENSE at 4°C

4) Solvent of Life Solution- two or more substances evenly mixed Solvent- Dissolving agent Solute- Whatever is dissolved in the solvent In an aqueous solution, the solvent is ALWAYS water

Solvent of Life Hydration shells- Molecules surrounded and attached to water - IE: NaCl - Na is slightly positive so the O in water will stick to this - Cl is slightly negative so the H in water will stick to this

Hydration shells

Solutions Some hydrophilic molecules/atoms can be considered a “colloid” = stable suspension of fine particles in water.

Solutions - Hydrophobic mixture- IE- Oil and water

Solutes - Solute [ ] (concentration) in aqueous solutions- - Mole = 6.02 x 1023 (Avagadro’s number) daltons in one gram - Molarity- Number of moles of solute per liter of solution

pH - pH - The hydrogen in an aqueous solution shifts from one O to another O. This shift will leave behind one electron. - H ion (H+)- Proton with a +1 charge - Water that lost its proton is called a hydroxide ion (OH-) and has a -1 charge.

pH An H+ proton can bond to another water molecule forming H3O+ (hydronium ion) - In pure water, H+ and OH- are usually about equal = neutral. H2O   H+ + OH-

pH

pH Acid- Donates H+ to a solution (more H+ than OH-) - Bases- Reduces total amount of H+ by accepting hydrogen ions. (fewer H+ than OH-)

pH - pH scale- In an aqueous solution at 25°C it is the product of H+ x OH- which will equal 1-14

pH Neutral = [H+] = 10-7 = [OH-] = 10-7 pH= -log [H+]. If neutral then –log 10-7 = -(-7) = 7

pH Simplified- -IE- A solution with a pH of 8 would have a H+ concentration of 10-8 M. -There is a tenfold difference for every step up and down scale.

pH Buffers- Minimize the change in the [ ] of H+ and OH- - Accepts H+ ions from a solution when in excess and donates them when they are low (IE- Carbonic acid in our blood) - Usually a molecule that has an acid/base pair - Most organisms need a pH of around 7 at all times.

A scientist created solutions of 0. 8M, 0. 6M, 0. 4M, and 0 A scientist created solutions of 0.8M, 0.6M, 0.4M, and 0.2M glucose, but did not label them. After realizing the error, the scientist randomly labeled the flasks containing these four unknown solutions as Flask A, Flask B, Flask C, and Flask D. Design an experiment, based on the principles of diffusion and osmosis, that the scientist could use to determine which of the flasks contain each of the four unknown solutions. Include in your answer: a) a description of how you would set up and perform the experiment; b) the results you would expect from your experiment; c) an explanation of those results based on the principles involved. (Be sure to clearly state the principles addressed in your discussion.)