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Water and Its Properties Honors Biology Ms. Kim. Water Water is composed of one atom of oxygen and two atoms of hydrogen held together by covalent bonds.

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Presentation on theme: "Water and Its Properties Honors Biology Ms. Kim. Water Water is composed of one atom of oxygen and two atoms of hydrogen held together by covalent bonds."— Presentation transcript:

1 Water and Its Properties Honors Biology Ms. Kim

2 Water Water is composed of one atom of oxygen and two atoms of hydrogen held together by covalent bonds (H2O) Water is a Polar Molecule  unequal distribution of charges One side is more positive One side is more negative When water molecules are close, their opposite sides are attracted to each other because of polarity This attraction between water molecules is responsible for most of the properties of water.

3 Polar and Nonpolar Molecules Polar Molecule – Unequal distribution of charges – One side is more positive – One side is more negative – Dissolves in water – Ex: Water Nonpolar Molecule – no separation of charge, so no positive or negative poles are formed. – Do not dissolve in water – Ex: CO2, O2, lipids  Think of the interaction of two magnets and how they either are attracted to each other or repel.

4 How do water molecules interact with each other? Polar water molecules can be attracted to each other The hydrogen atom with its’ partial positive charge (+) is attracted to the oxygen atom (partial negative charge) of a different water molecule! – This is known as a hydrogen bond

5 Hydrogen Bonds Bonding between molecules Very weak, but very important for the various characteristics of of water…

6 Covalent bonds internally hold a water molecules together – Different water molecules are held together by hydrogen bonds – very weak bonds Hydrogen Covalent

7 5 Characteristics of Water 1. Cohesion 2. Adhesion 3. High Specific Heat 4. Less Dense as a Solid 5. Water is a terrific solvent

8 Water Properties **H-bonding is responsible for these properties 1. Cohesion (“co-” means “together”) – the attraction between molecules of the same substance (water) – Tendency of molecules of the SAME “kind” to stick together 2. Surface Tension: – Measure of how difficult it is to stretch or break the surface of a liquid/ resist an external force. H 2 O has high surface tension Due to H-bonds

9 Water “sticks” to itself

10 Surface tension – another type of cohesion – a measure of how difficult it is to stretch or break the surface of a liquid – Water molecules form a “barrier” by H- bonding together – Water does NOT pull apart very easily  acts like elastic

11 2. Adhesion Adhesion = The type of attraction that happens between two different molecules – Glass, soil, plant tissue, cotton, etc. Forms stronger bonds than cohesion Example: – Meniscus forming on graduated cylinder! – Capillary action- seen in plants, trees and with straws too!

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13 Cohesion & Adhesion Acting Together – Helps pull water up through the microscopic vessels of plants is Called capillary action

14 Another Example of Cohesion and Adhesion… Cohesion Adhesion

15 The temperature of water does not increase or decrease easily Water has to absorb more heat energy to increase overall temperature compared to other compounds – Ex: Lake Michigan is really cold until ~ August…it takes a long time to warm up!! Helps to regulate cell temperatures in organisms High Specific Heat

16 Water has a high specific heat so its temperature does NOT fluctuate very much  allows life to live in water – moderate Earth's climate by buffering large fluctuations in temperature.

17 How come icebergs float?

18 4. Low Density in Solid Form Allows for insulation of bodies of water by floating ice Solid water (i.e.-ice) – Is less dense than liquid water – Floats in liquid water Since ice floats in water  – Life can exist under frozen surfaces of lakes/polar seas

19 Ice floats because ice is less dense than liquid water! – This is because the H bonds hold the water molecules farther apart than in liquid water

20 The hydrogen bonds in ice – Are more “ordered” than in liquid water, making ice less dense Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable

21 5. Water as a Solvent What is a solution? –A solution is a mixture of substances looks the same throughout Made up of a solute and a solvent  Water is a GREAT solvent (Water is the universal solvent)  Solute – gets dissolved (Hot Cocoa mix)  Solvent – does the dissolving (Water)  Solution – uniform mixture of two or more substances

22 Hydrophilic and Hydrophobic Substances A hydrophilic substance – Has an affinity for water – Water “loving” – Dissolves in water – Example: salt and sugar A hydrophobic substance – Does not have an affinity for water – Water “fearing” – Does NOT dissolve in water – Example: Oil

23 REVIEW Where is the Polar Covalent Bond in water? What is the difference btw a “POLAR COVALENT BOND” and a “NONPOLAR COVALENT BOND?

24 Acids and Bases An acid – compound that releases/donates a proton (H+) when dissolved in water Increases H+ concentration in solution Ex: HCl A base – compound that accepts H+ and removes them from a solution – Is any substance that reduces the hydrogen ion concentration of a solution The more basic the solution, the higher the OH- concentration Ex: NaOH pH – Measure of acidity or alkalinity of an aqueous solution

25 What is the pH scale? ✿ Identifies acids and bases ✿ Indicates concentration of H + ions in a solution

26 How do you read the pH scale? ✿ pH of 7 ❀ Neutral ❀ Concentration of OH - and H + are equal ❀ Ex – Water ✿ pH 1 – 6.5 ❀ Acid ❀ More H + than OH - ❀ Ex – Lemon juice / HCl ✿ pH 7.5 – 14 ❀ Base ❀ More OH - than H + ❀ Ex – Baking soda / ammonia

27 What is a buffer? ✿ Buffers prevent drastic changes in pH ✿ Buffers: weak acids or bases that can react with strong acids or bases to prevent sudden changes in pH ✿ Why are buffers important? ❀ Key in regulating our urinary, circulatory, and blood pH ❀ Necessary in maintaining homeostasis

28 the lower the pH the stronger the acid the higher the pH the stronger the base pH 7.0 is neutral

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30 Acid precipitation – Can damage life in Earth’s ecosystems More acidic Acid rain Normal rain More basic

31 Thermal Energy Thermal energy is the energy that is generated and measured by heat.


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