Foundation ScienceToday’s Lesson: Properties of Water
Water is a Polar MoleculeWater molecules are polar.Polar = has a positive sideand a negative side.The negative part of awater molecule isattracted to the positivepart of another.
Water Forms Hydrogen BondsThe bonds formed betweenwater molecules are calledhydrogen bonds.Hydrogen bonds betweenmolecules of water is whatcauses water’s surface tension
Water’s Boiling and Freezing PointsWater is considered to be so important that the scale weuse to measure temperature was set according to water!Water boils at 100° CelsiusWater freezes at 0° CelsiusFrozen water (ice) is less dense than liquid water, whichis why ice floats.Water is most dense (heaviest) at 4° Celsius.
The Science of Cooking with WaterWhat gets hotter, steam or boiling water?The answer is steam. Boiling water can only reach 100° Celsius.Steam has passed into a vapor and can be heated higher than100° Celsius.Steaming vegetables can be healthier and more delicious becauseit doesn’t rinse away all the vitamins, and FASTER too because thesteam can be hotter than 100° Celsius.
The Science of Cooking with WaterCan we make water boil hotter than 100° Celsius?YES! Pressure increases the boiling point. Water willboil at a lower temperature up at the top of amountain (=less pressure from atmosphere) than atthe bottom of the mountain.So, why do you think people use a pressure cooker?It is so they can cook things in water that is hotterthan 100° Celsius, because the lid on the pressurecooker creates pressure inside the pot.
Boiling Water and SpaceHow much pressure is there in space?Space has very little, to no pressure.So what is a space suit really for?A human body is about 70% water. With no pressure, all thewater in a human would boil and turn to steam! NASA says thata person could live about 1 minute in space without a suit.Note: (don’t need to write in notes) a man accidentally exposedto a vacuum at NASA lost consciousness after about 14 secondsdue to lack of oxygen. He said his last memory was “the waterbeginning to boil on his tongue”. You will NOT explode withouta spacesuit in space says NASA.
More about Boiling WaterHow do you know when water is at 100° Celsiuswhen cooking?When the first bubble of air floats all the way tothe top of the water.Do you need to make water boil like crazy for itto be 100° Celsius?No! Just enough for the first bubbles to be riseto the top. After that, it only needs a little heatto stay at 100° Celsius.What are the bubbles in boiling water made of?Steam (=water vapor)
Capillary ActionCapillary action occurs when water goes upagainst the forces of gravity. GravityWithout hydrogen bonds, capillary actioncould not occur. Capillary ActionCapillary action is how plants and treestransport water from the roots to leaveswhere photosynthesis occurs.
How Does Capillary Action Occur?1) Adhesion is the attraction between waterand other objects. Example of Water AdhesionAdhesion allows water to stick to the sidesof the tube (can be a straw or inside aplant).2) Cohesion is water being attracted to itselfdue to its hydrogen bondsAdhesion and cohesion lead to water’s capillary action
Water has a Very High Specific Heat CapacitySpecific heat is how much energy is required to heat a substance.Water needs a LOT of energy to be heated, so WATER HAS A VERYHIGH SPECIFIC HEAT CAPACITY.To heat things you need to make the molecules move faster. It is hard to make water molecules move fast because its hydrogen bonds keep the molecules stuck together.
Is Water an Acid???Pure water is not an acid (not acidic).BUT, when water is exposed to air, it comes in contact with carbondioxide (CO2) and forms a weak acid called carbonic acid:CO2 + H2O H2CO3Carbonic acid can dissolve rock and things like cement. Water can turn slightly acidic, and over time, make holes in rock
Is Water an Acid??? Over time, water is responsible for carving out large cave systems like Carslbad Caverns. Water is also what made the stalagmites and stalactites. So, YES, water can be an acid.Water has Carlsbad Cavernsthe power todissolvelimestone
QUESTIONS (2 Points Each)1. Tell me 3 things water could NOT do if it was not a polar molecule.2. Draw a diagram of a hydrogen bond. Label the oxygen and hydrogen atoms and the hydrogen bond.3. If you wanted to make a 5 liter bottle of water as heavy as possible, what temperature would you bring the water to?4. Where will water boil hotter, Bangkok or Chiang Mai?5. True or False: A pressure cooker can cook faster because the water inside is able to get hotter than 100° Celsius.6. Tell me how you know when water is 100° Celsius when cooking.7. What would happen to a human in space without a spacesuit?8. Draw a diagram of capillary action in a plant.9. What is adhesion?10. What is cohesion?11. Tell me one reason why water’s high specific heat may be important for a human body.12. You are walking on the street and see some holes in the sidewalk. Explain to me how water may have caused these holes.13. Why will it save energy to steam vegetables instead of boiling them?