Water 2.2 Mr. McGee, IB Biology (HL)

By the End, You Will Understand: Water molecules are polar and hydrogen bonds form between them. Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water. Substances can be hydrophilic or hydrophobic.

By the End, You Will Have the Following Applications and Skills: Compare the thermal properties of water with those of methane. Use of water as a coolant in sweat. Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water.

Theory of Knowledge (TOK) Claims about the “memory of water” have been categorized as pseudoscientific. – What are the criteria that can be used to distinguish scientific claims from pseudoscientific claims?

Polarity of Water Polar molecules are caused due to uneven charges over a molecule. The polarity of water allows substances to dissolve well in water. Non-polar or neutral substances have no charges, therefore, they are NOT attracted to water or dissolve.

Diagram of a polar molecule:

Nearly 70% of your body is composed of water. Water has specific properties that make it very important for life.

Water is able to do all that it does because of hydrogen bonding.

Water Stores Heat Efficiently Water has a high heat capacity. – Water can absorb and release a huge quantity of heat without changing temperature. – Important for life because: We need to maintain our body temperature on hot and cold days. Water helps maintain homeostasis.

Water Bonds Itself to Other Substances Adhesion = Water sticking to substances. Cohesion = Water sticking to itself, forming droplets

Water Dissolves Many Substances Many substances dissolve in water. This means they break down and spread out evenly into a solution. Because substances dissolve in water, they can more easily move within and between cells. (For example, sugar cannot be delivered to cells if it were still crystal-like and not dissolved in water).

High Heat of Vaporization Water vaporizes (turns to a gas) at a far higher temperature than comparative liquids. It is able to therefore carry heat away from the body.

Acids & Bases Water (H 2 O) sometimes breaks apart to form H+ and OH-. (hydrogen ion and hydroxide) H+ (hydrogen ions) are necessary to measure in biology because they are highly reactive.

Water can Dissociate Sometimes… Water breaks apart, forming H + and OH -. O HH Water! (H 2 O) Boom!

Water can Dissociate Sometimes, water breaks apart, forming H + and OH -. O H H OH - H+H+

O HH O HH O HH O HH What is pH? pH is a measurement of free hydrogen ions [H + ] in a solution. Measurements are made on a scale of H H H H H H H H H H H Ahhhhh! Hydrogen Ions! H H HH H H H H H H H H H H H H H H H H H H

What is pH? Why is measuring pH important to biologists? – Because these free H+ are VERY REACTIVE! – Remember, living organism are very sensitive and must maintain delicate homeostasis… H Ugh, you’ve gotta be kiddin’ me! It’s Kanye, interrupting us again! “Dude, what’s the big deal? It’s a just a hydrogen ion…” (Oh, and Beyoncé had the best video)

Free ions are very reactive! H Hydrogen Ion Reward: Homeostasis For being aggressive; reacting with everything it encounters! Ion may alter your pH!

What are Acids/ Bases? It’s the end of the world! Ahhh!

Acids: Substances that add H + to a solution. Bases: Substances that remove H + from a solution. What are Acids/ Bases? Acid(Neutral)Base H

pH Scale ranges from 0-14 – 0-7 is acidic – 7-14 is basic – 7 is neutral pH Scale Acid(Neutral)Base

Acid(Neutral)Base Pure H + Solution No H + in Solution

1. What is the strongest acid on this chart? 2. The weakest acid? 3. What is the strongest base? 4. Weakest base?

Assignment None.