Presentation on theme: "Water. The search for life is really a search for water. We’ve met and discovered many organisms that have surprised us in their abilities to survive."— Presentation transcript:
The search for life is really a search for water. We’ve met and discovered many organisms that have surprised us in their abilities to survive and even thrive in many harsh and inhospitable environments. Mars video
Why? The water molecule
1. Water is clingy
Polarity Due to the unequal sharing of electrons in a covalent bond
Hydrogen bonding… Leading to the property of cohesion (the attraction among like molecules)
Surface Tension How difficult it is to stretch or break the surface of a liquid.
Water is not the only substance with charged regions, so the charged areas of the water molecule can be attracted to oppositely charged areas on other types of molecules resulting in adhesion…the attraction of unlike molecules.
Capillarity (capillary action) Water conducting cells 100 µ m Figure 3.3 The combined effects of cohesion and adhesion
2. Water absorbs and releases heat s-l-o-w-l-y.
Heat Is a measure of the total amount of kinetic energy of the molecules Temperature Measures the average speed of one molecule of the substance. Think of a cool swimming pool vs a hot cup of tea. Which has the higher temperature? Which has more heat energy?
The specific heat of a substance: The amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1’C.
The specific heat of water is 1 cal/g ‘C So… A calorie is the amount of heat required to raise 1g of water by 1’C. A kilocalorie (kcal, or Calorie) is the amount of heat required to raise 1kg of water by 1’C. Water has an extremely high specific heat, which allows it to minimize temperature fluctuations on the Earth and in your body.
Have you ever gone in the ocean on a nice, hot day in early June? What about a mildly cool day in mid- September? Most deserts are extremely hot during the day, but what happens when the sun goes down?
Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler. The Gulf Stream redistributes the heat energy from the equator to the higher latitudes of Western Europe.
A similar thing happens when you perspire…each droplet of sweat contains a large amount of heat energy that is sent to the surface of your body to be released to the air around you as it turns to a gas. You warm up the air when you sweat! Evaporative Cooling
In order for one gram of liquid water to turn into a gas at room temp, 580 calories of heat energy must be absorbed. Again, water has a very high heat of vaporization compared to most other substances. Remember…breaking bonds releases energy (exergonic) and forming bonds requires energy (endergonic). Heat of Vaporization
3. Solid water FLOATS!!!
Ice is less dense than liquid water and therefore floats on it. It serves to insulate the water below the ice. (Ponds are not frozen to the bottom!...life continues all winter). Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond Figure 3.5 To form the crystal lattice, water molecules “push away” from each other.
4. Universal Solvent Because water is polar it can dissolve most charged solutes and ionic compounds.
Cl – – – – – Na + Positive hydrogen regions of water molecules cling to chloride anions (Cl – ) – – – – – – Na + Cl – Figure 3.6 Negative oxygen regions of polar water molecules are attracted to sodium cations (Na + ). Hydration Shell
(a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva (c) Ionic and polar regions on the protein’s Surface attract water molecules. ++ –– Figure 3.7 This oxygen is attracted to a slight positive charge on the lysozyme molecule. This hydrogen is attracted to a slight negative charge on the lysozyme molecule.
So what if I need to dissolve a non-polar compound? Use a non-polar solvent. Remember the rule “Like dissolves like”.
A mole Represents an exact number of molecules of a substance in a given mass How many moles are there in 20 grams of hydrogen? H’s atomic mass ~ 1 Moles = mass/relative mass = 20/1 = 20 moles. Molarity Is the number of moles of solute per liter of solution Measures concentration
5. Acidity and Alkalinity H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + Figure on p. 34 of water dissociating Water dissociates into hydronium and hydroxide ions
Acids; increase hydrogen ion concentration Bases; decrease hydrogen ion concentration (increase hydroxide ion concentration)
Remember that pH is based on the negative log of the concentration of hydrogen ions, so a higher pH number is a lower concentration of ions.
Buffers in the blood… The internal pH of most cells is 7 Human blood is about 7.4 Buffers are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution They consist of an acid-base pair that either donates or accepts hydrogen ions in reversible reactions. Living things make the buffers they need to maintain homeostasis.