KEY CONCEPT Water’s unique properties allow life to exist on Earth.

Life depends on hydrogen bonds in water. Water is a polar molecule. Polar molecules have slightly charged regions. O H _ + Nonpolar molecules do not have charged regions. Hydrogen bonds form between slightly positive    hydrogen atoms and slightly negative atoms.

Hydrogen bonds are attractions due to charged regions

Hydrogen Bond Hydrogen bonds are found among water molecules, and hydrogen bonds are found in many other molecules, such as proteins and DNA (deoxyribonucleic acid). Protein DNA

Hydrogen bonds are responsible for three important properties of water. high specific heat cohesion adhesion

Properties Related to Hydrogen Bonding High Specific Heat: water must absorb more heat energy to increase in temperature because hydrogen bonds are relatively strong among water molecules. This property is very important in cells because the processes the usable chemical energy inside cells release a great deal of heat. Water absorbs the heat, which helps to regulate cell temperatures.

Properties Related to Hydrogen Bonding Cohesion: The attraction among molecules of a substance. Water molecules “stick” together because of the cohesion of hydrogen bonds.

- - (Sharing Electrons) - + + + + Cohesion + +

Properties Related to Hydrogen Bonding Adhesion: The attraction among molecules of different substances.

Properties Related to Hydrogen Bonding Adhesion: The attraction among molecules of different substances. Adhesion is the reason for the upward curve of water on the surface of a test tube.

How are hydrogen bonds similar to ionic bonds? Hydrogen bonds are attractions due to charged regions; ionic bonds are bonds formed by the attraction of oppositely charged ions.

Surface Tension Each water molecule experiences a pull from other water molecules from every direction. Water molecules at the surface do not have molecules above the surface to pull at them. These water molecules have more pull from the water below than the surface above. This difference in force packs the water molecules at the surface closer together than they are inside the liquid. The thin, dense layer of molecules produces the phenomenon called surface tension.

How does soap disrupt water’s surface tension? Soap molecules are made up a polar, hydrophillic (“water loving”) head and a long hydrophobic (“water fearing”) tail, also known as a hydrocarbon chain. The molecules' two ends make it able to break through the surface tension of water. Hydrophobic Chain (hydrocarbon tail) “water fearing” Hydrophilic Head “water loving”

How does soap disrupt water’s surface tension? The end of the soap molecule (hydrophobic chain), which attaches to dirt and fat (grease), repels water molecules. By attempting to move away from the water molecules, the hydrophobic ends of the detergent molecules push up to the surface. This weakens the hydrogen bonds holding the water molecules together at the surface. The result is a break in the surface tension of the water.

How does soap and detergents clean?

How Soap Works https://www.youtube.com/watch?v=Nxkjn-XhgE0

Water cohesion, adhesion and surface tension lab You will conduct an experiment and apply your knowledge of the chemical properties of water to understand its cohesive behavior.

Many compounds dissolve in water. Molecules and ions cannot take part in chemical processes inside cells unless they can dissolve in water. Important materials such as sugars and oxygen cannot be transported from one part of an organism to another unless they are dissolved in blood, plant sap, or other water based fluids. Many substances dissolve in the water in your body.

Many compounds dissolve in water. A solution is formed when one substance dissolves in another. A solution is a homogeneous mixture of two (2) or more substances. Solvents dissolve other substances. It is the part of the solution that is present in the greatest amount (like water) Solutes dissolve in a solvent. the part that is present in a lesser amount (like salt)

A solution can be a solid, liquid or gas. It only has one phase A solution can be a solid, liquid or gas. It only has one phase. That is, once the salt is dissolved in the water you see only the liquid, not the salt and water separately. In a solution the solute remains uniformly distributed throughout the solution and will not settle out with time. So if you take a sample, it will be exactly the same as the remaining solution. Every part of a solution has exactly the same properties and composition as every other part.

A homogeneous mixture is simply any mixture that is uniform in composition throughout.

Other examples of solutions (homogeneous mixtures) Syrup: Sugar in water Vinegar: Acetic acid in water Shampoo: Soaps and surfactants in water Chocolate milk: Chocolate powder in water or milk Febreeze: water, alcohol, odor eliminator derived from corn, fragrance Steel: Iron ore, carbon and other elements

Plasma Plasma is the clear, straw-colored liquid portion of blood that remains after red blood cells, white blood cells, platelets and other cellular components are removed. It is the single largest component of human blood, comprising about 55 percent, and contains water, salts, enzymes, antibodies and other proteins. Composed of 90% water, plasma is a transporting medium for cells and a variety of substances vital to the human body. Plasma carries out a variety of functions in the body, including clotting blood, fighting diseases and other critical functions.

Composition of air

Rule of Thumb Like dissolves like! Polar solvents dissolve polar solutes. Example: Water and salt. Nonpolar solvents dissolve nonpolar solutes. Example: Gasoline and benzene Polar substances and nonpolar substances generally remain separate. Example: Olive oil and balsamic vinegar. Rule of Thumb Like dissolves like!

Understanding pH

pH: Power of Hydrogen

In chemistry, pH is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. A solution’s acidity (H+ ion concentration) is measured by the pH scale. The pH scale reads from 0 to 14. There is an inverse relationship between the concentration of hydrogen ions (H+) and pH. A solution with a pH of 0 is very acidic and has a high concentration of H+ ions. A solution with a pH of 14 is very basic (alkaline) and has a low concentration of H+ ions.

Some compounds form acids or bases. An acidic substance releases a hydrogen ion (H+) when it dissolves in water. high H+ concentration pH less than 7 more acidic stomach acid pH between 1 and 3

Common Examples of acidic substances: Soda Vinegar Meats Orange juice Energy drinks Stomach acid

A basic substance removes hydrogen ions from a solution. low H+ concentration pH greater than 7 bile pH between 8 and 9 more basic

Common Examples of basic substances: Soap Toothpaste Bleach Cleaning agents Ammonia Sodium hydroxide (drain cleaner)

A neutral solution has a pH of 7. pure water pH 7

The pH of a solution depends on the concentration of H+ ions. The concentration of H+ and OH-- ions varies depending on how acidic or basic (alkaline) a solution is. Neutral High concentration of H+ ions. Low concentration of OH– ions. Low concentration of H+ ions. High concentration of OH– ions. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Strong Acid Weak Acic Weak Alkali (Base) Strong Alkali (Base)

Why is pH important in biology? Most cells can only survive in a certain pH range. For example, human blood has a pH of about 7.4, slightly alkaline (basic). A small change in pH can disrupt the processes in your cells. Any higher or lower and the blood cells would be injured or killed. A blood pH greater than 7.8 or less than 6.8, for even a short time, is deadly.

Answer questions on page 43 Summarize – refer to figure 2.9 Describe the relationship between the H+ concentration and pH value. Answer: The higher the H+ concentration, the lower the pH. Apply Cells have higher H+ concentrations than blood. Which has a higher pH? Why? Answer: Blood has a higher pH because it has a lower concentration of H+ ions. 2.2 Assessment, questions # 2, 4, Answer to # 2: Compounds that have charges, such as ionic compounds and polar molecules, will dissolve in water.

DO NOT USE EYEDROPPERS AS MINI WATER GUNS!!! Lab Safety Rules Always wear safety goggles when experimenting with chemicals (soap). Never taste chemicals (or other substances) used for a lab experiment. Keep lids on all containers when not in use. Clean up spills immediately. If any substance gets into your eyes or in a cut on your skin, notify me and follow my directions. Wash your hands before and after an experiment. Clean up you lab area and materials after an experiment and return materials to their proper location. DO NOT USE EYEDROPPERS AS MINI WATER GUNS!!!