Properties of Water - Califf 2024 PDF

What makes water so special?  Water is everywhere! The Earth is ~71% water 60-80% human cells Water is a polar molecule Molecules of water are held together by hydrogen bonds  Properties of Water A water molecule (H2O) is made up of three atoms - one oxyge...

What makes water so special?  Water is everywhere! The Earth is ~71% water 60-80% human cells Water is a polar molecule Molecules of water are held together by hydrogen bonds  Properties of Water A water molecule (H2O) is made up of three atoms - one oxygen and two hydrogen H O H  Water is a polar molecule The oxygen end “acts” negative Causes water to be The hydrogen end “acts” POLAR positive 🡪 Like a magnet.  Hydrogen Bonds exist between Water Molecules Weak bond, but strong in great numbers *Formed between a very electronegative atom of a polar molecule (like water) and a hydrogen atom Covalent bonds within water molecules - Powerful bond  Properties of Water 1. Cohesion 2. Adhesion 3. Less Dense as a Solid 4. High Heat Capacity 5. Universal solvent 1 & 2: Cohesion & Adhesion. Sticky Cohesion: sticking together of like molecules (water is attracted to itself) – Surface tension; water beading  Let’s try it! #1 Cohesion Question 1: How many drops of water fit on the head of a penny? - Use a pipet to slowly drop water onto a penny counting each drop. - Repeat this procedure with a new penny using oil. How does this investigation differ? - Thoroughly rinse and dry the pennies.  Let’s try it! #2: Density & Surface Tension -Add some water to a petri dish - Place a small square (~2 in x 2 in) of aluminum foil on the surface of the water.Does it float? - Press the square down into the water. Does it float? -- Take the square of foil and crumple it into a ball. Place it back in the water. Does it float? - Throw away the foil. - Now try the PAPERCLIP! Look at it closely from the side. What do you notice? 1 & 2: Cohesion & Adhesion Sticky Adhesion: sticking together of unlike molecules – Capillary action: Draws water up the roots of a plant – Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. – Water molecules will “tow” each other along when in a thin glass tube.  Let’s try it! #3 -Place 2 drops of water on one end of a glass microscope slide and 2 drops of oil on the other end, use the properly labeled pipet for each!! The drops cannot touch. -Hold the capillary tube vertically and put one end in the water. Watch what happens after ten seconds. -Repeat with oil, but use a new capillary tube. What is different? -Place used tubes in the red “waste” cup and put the slides in the soapy water dish. 3: Less dense as a solid – Ice insulates ponds Which is ice and which is water? Why is this bad for cells? 4: High Heat Capacity Water resists temperature change, both for heating and cooling. Moderates the temperature on earth and in our bodies Water molecules are held tightly together by H bonds; requires more heat energy to move the molecules Ability to maintain a steady state despite changing conditions. 5: Universal solvent Water is usually part of a mixture Good solvent: Water is the solvent of LIFE! Solute – substance that is dissolved Solvent – fluid that dissolves a solute Solution = solute + solvent Ex: Iced Tea – water is the solvent; tea & sugar the solutes  Solutions Water is the solvent, salt is the solute 🡪 salt water is the solution  Solutions Water’s polarity allows it to dissolve both ionic compounds & other polar molecules. 5: Universal solvent Takes part in reactions – Hydrolysis = digestion of macromolecules Let’s try it! #4 Will it dissolve? Use your disposable pipette to fill both - test tubes with one pipet full of water. Add 1 pipet full of oil to one tube and 1 pipet full of alcohol to the next one. Gently mix. What happens? - Let’s look at the models of oil and - alcohol. Mix the models with the water model. What do you notice? How does this explain what you observed in the test tubes?  Homeostasis! Water is important to this process because: a. Makes a good insulator b. Resists drastic temperature changes (Coolant) c. Ice protects against temperature extremes (insulates frozen lakes) d. Universal solvent e. Carries nutrients & wastes in our blood f. Helps with chemical reactions  Acids, Bases and pH One water molecule is made of two ions: Hydrogen (H+) and a Hydroxide Ion (OH-) + - H2 O ⮀ H + OH Hydrogen Ion Hydroxide Ion Acid Base  Acids and Bases Acid: A solution with lots of H+ ions pH: 0-7 is acidic Gastric juice, saliva Base: A solution with lots of OH- ions pH: above 7 – 14 is basic Not common in the human body Neutralization Equal amounts of acid and base of same concentration give a neutral pH of 7 H+ + OH- 🡪 H2O  The pH Scale Indicates the percent of H+ ions Ranges from 0 – 14 pH of 7 is neutral  Human biology and pH Your blood maintains a pH of 7.35 – 7.45 (slightly basic) – Balance is maintained by buffers in blood, breathing, and urinating  Let’s try it! #5 Use the pH strips to determine the pH of the following. Dip the end of the pH paper into the fluid and compare to the chart provided. - Water: - Detergent: - Coke: - Vinegar: - Hydrogen Peroxide: Quick Quiz  Quick Quiz 1.Draw a water molecule with labeled atoms and charges. 2.What is the property called that describes water sticking to itself? 3.What makes a solution acidic? 4.What has a higher pH, bleach or lemon juice? 5.Why do we sweat?  Quick Quiz 1.Draw a water molecule with labeled atoms and charges.  Quick Quiz 1.Draw a water molecule with labeled atoms and charges. 2.What is the property called that describes water sticking to itself?  Quick Quiz 1.Draw a water molecule with labeled atoms and charges. 2.What is the property called that describes water sticking to itself? 3.What makes a solution acidic?  Quick Quiz 1.Draw a water molecule with labeled atoms and charges. 2.What is the property called that describes water sticking to itself? 3.What makes a solution acidic? 4.What has a higher pH, bleach or lemon juice?  Quick Quiz 1.Draw a water molecule with labeled atoms and charges. 2.What is the property called that describes water sticking to itself? 3.What makes a solution acidic? 4.What has a higher pH, bleach or lemon juice? 5.Why do we sweat?