Lecture #12 Water and Its Properties Honors Biology Ms. Gaynor

Water (H 2 O) Characteristics 1.) Oxygen has a partial – end 2.) hydrogens have partial + end 3.) hydrogen is attached to oxygen by a covalent bond 4.) Water is a polar molecule

What is “polarity”? A molecule that has different charges on each end or “pole” A molecule that has different charges on each end or “pole” Asymmetrical ends = polar Asymmetrical ends = polar Water’s polarity allows for LOTS of hydrogen bonding Water’s polarity allows for LOTS of hydrogen bonding partial + ends bind with partial - ends

Water Properties Water Properties 1. Water demonstrates Cohesion (“co-” means “together”) – water molecules H- bond to neighboring water molecules – Partial - & partial + ends attract each other – water “sticking” to itself –Examples: transpirational-pull, surface tension

Water “sticks” to itself

Transpirational Pull Transpirational Pull  a result of cohesion – Helps pull water up through the microscopic tubes of plants

Surface tension Surface tension – a measure of how hard it is to 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

2. Water demonstrates Adhesion Water molecules H- bond to different molecules Water molecules H- bond to different molecules –Partial - & partial + ends of water attract to ends of other molecules Examples: water “sticking” to stuff (i.e.-towels, clothes, paper, glass) Examples: water “sticking” to stuff (i.e.-towels, clothes, paper, glass)

Cohesion & Adhesion Acting Together Cohesion & Adhesion Acting Together – Helps pull water up through the tubes – Called capillary action

Another Example of Cohesion and Adhesion… Cohesion Adhesion

3. Water has a HIGH heat capacity Water changes temperature very slowly Water changes temperature very slowly –Allows large bodies of water to remain stable in temperature even when temperature of air changes Need to use A LOT of energy to raise or lower temp of water Need to use A LOT of energy to raise or lower temp of water

Water has a High Specific Heat WHY IS THIS PROPERTY IMPORTANT TO BIOLOGY? 1.Contents 1.Contents of cells are mostly water and are unlikely to freeze 2.Helps 2.Helps maintain homestasis (ex: thermoregulation) 3.Helps 3.Helps moderates Earth's climate by buffering large fluctuations in temperature.

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

Separated by 105 o when in the gaseous or liquid phase Separated by 105 o when in the gaseous or liquid phase – o when ice Polar Structure

Hydrogen bonds in ice Hydrogen bonds in ice –Are more SPACED APART than in liquid water, making ice less dense Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable

5. Water is an Excellent Solvent Water is a great solvent (“dissolver”) Water is a great solvent (“dissolver”) It can form aqueous (“watery”) solutions very easily! It can form aqueous (“watery”) solutions very easily! –IMPORTANT TO BIOLOGY…MOST biochemical reactions occur in water!!!

Solution = a UNIFORM mixture of 2+ substances – –LOOK the same (uniform) throughout Solvent = substance that is doing the dissolving – –The “dissol v er” Solute = substance(s) getting dissolved Ex: Ex: salt water solution

The different ends of the polar water molecule can interact with ionic compounds (the solutes) and dissolve them The different ends of the polar water molecule can interact with ionic compounds (the solutes) and dissolve them Negative oxygen regions of polar water molecules are attracted to sodium cations (Na + ) Cl – – – – – Na + Positive hydrogen regions of water molecules cling to chloride anions (Cl – ) – – – – – – Na + Cl –

Hydrophilic and Hydrophobic Substances A hydrophilic (polar) substance A hydrophilic (polar) substance – Is attracted to water – Water “loving” A hydrophobic (nonpolar) substance A hydrophobic (nonpolar) substance – Not attracted to water – Water “fearing” “Like mixes with like”

Water can separate in solutions… Water can split into 2 parts Water can split into 2 parts 1. Hydrogen ion (H + ) 2. Hydroxide ion (OH - ) hydroxidehydrogen ion

Acids and Bases An acid An acid –increases the hydrogen ion (H+) concentration of a solution A base A base –reduces the hydrogen ion (H+) concentration of a solution pH pH –Measure of acidity or basic of an aqueous solution

The pH Scale The pH of a solution The pH of a solution –determined by the relative [ ] of H + ’s –high [H + ] = acid –low [H + ] = base –Lower H+ [ ] = higher OH- [ ]

The pH scale and pH values of various aqueous solutions The pH scale and pH values of various aqueous solutions Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ] Neutral [H + ] = [OH – ] Oven cleaner pH Scale Battery acid Digestive (stomach) juice, lemon juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Pure water Human blood Seawater Milk of magnesia Household ammonia Household bleach Each increase or decrease is 10x

Acids = low pH #’s Acids = low pH #’s – HIGH [ ] of H+ Bases = High pH #’s Bases = High pH #’s – HIGH [ ] of OH- Remember…. A…..B…. In the alphabet and 1….14 A…..B…. In the alphabet and 1….14 A= 1 st letter (H+ has 1 letter) A= 1 st letter (H+ has 1 letter) B= 2 nd letter (OH- has 2 letters) B= 2 nd letter (OH- has 2 letters)

Buffers Buffers Buffers –substances that minimize changes in [ ] of H+ and OH- ions in a solution Consist of an acid-base pair that reversibly combines with hydrogen ions Consist of an acid-base pair that reversibly combines with hydrogen ions Most living cells must remain close to pH 7 Most living cells must remain close to pH 7 –Need biological buffers to regulate systems (absorbs/releases excess H+) Most important buffer in humans = bicarbonate ion (Ex: H 2 CO 3 ) Most important buffer in humans = bicarbonate ion (Ex: H 2 CO 3 )