Water & pH Chapter 3 pgs

Importance of Water 71% of Earth’s surface is ocean water 66% of human weight Only common substance to exist in three forms: solid, liquid and gas

How does water work?  Oxygen atom is attracted to the hydrogen atoms  Resulting bonds are Hydrogen Bonds  Individual hydrogen bonds are quite weak, but many working together are very strong  Hydrogen bonds that give water its unique properties

Unique Properties of Water  Solid form is less dense than the liquid form  Absorbs lots of heat without much change in temperature  Sticks to itself  Sticks to other things

Unique Properties of Water Ice floats: for most substances, the solid form is more dense than the liquid form and will sink. But for water, the solid form is less dense than the liquid form. Why is this important?

Unique Properties of Water Water has great capacity to absorb and store heat: “heat” and “temperature” are not the same things! For example: Corningware ® glass pot vs. aluminum pot of same weight were heated on two stove burner. Which one would heat up faster? The Corningware® pot can absorb more heat without changing in temperature much

Specific heat: the amount of energy required to raise the temperature of a substance by 1 o C  During the day in the summer, bodies of water (oceans and lakes) absorb heat from the sun and this keeps the surrounding air cooler  At night and during the winter, bodies of water give up heat and this warms the surrounding air So why is the desert have such extreme day-time vs. night- time temperature changes? In our bodies, absorb heat in the summer from the sun without overheating & in the winter we don’t immediately freeze when we go outside

Just for fun facts It takes more energy to heat water than many other molecules because of hydrogen bonds. 1 calorie of energy will increase the temperature of 1 gram of water by 1 degree C It only takes 0.6 calories to increase 1 g of alcohol by 1 degree & 0.2 calories to heat 1 g of table salt

Unique Properties of Water Cohesion Cohesion produces, or the tendency for the surface of the water to avoid being broken. Cohesion produces surface tension, or the tendency for the surface of the water to avoid being broken. Forms droplets

The strong hydrogen bonds of water allow water to be pulled up through the roots of a 100-meter tall tree The strong hydrogen bonds of water allow water to be pulled up through the roots of a 100-meter tall tree Why is cohesion important?

Unique Properties of Water Water molecules can stick to other things, or at least some other things For example: glass, paper, sugar, salt can mix with or stick to water. Hydrophilic = Those compounds that do not interact with water; such as salad oil, teflon, car wax = Hydrophobic

Hydrophilic Molecules Hydrophilic Molecules Hydrophobic Molecules Hydrophobic Molecules

What are acids and bases? Examples of acids: lemon juice, vinegar, tomatoes   Acid Examples of bases: ammonia, soap, oven cleaners   Base Measure the degree of acidic or basic by the pH scale

pH Scale   Neutrality (equal numbers of H+ and OH-) = 7   Acids = below 7   Bases = above 7   Each unit = 10 fold change

 The higher the pH, the more basic the solution  A solution that is basic is also referred to as an alkaline solution  The lower the pH, the more acidic the solution

Example: Vinegar has a pH of 3 If you add sodium hydroxide (NaOH), what will happen to the pH of your vinegar? If you add hydrochloric acid (HCl)?

Why do we care about pH?  Living organisms are sensitive to pH levels and an imbalance in pH can lead to DEATH!  Organisms have developed ways of keeping pH within normal ranges using an acid-base buffering system  Buffer = substances that minimized change in pH

Just for fun facts  The pH of our stomachs are around 1-2, so that foods can be broken down  The optimal pH for healthy skin and scalp is around 5 slightly acidic for resistance to infection and diseases  Soaps and shampoos are basic and thus can cause drying of the skin and scalp  So when you see a “pH-balanced” shampoo or soap, the manufacturer has lowered the pH so its closer to normal skin pH