Foundation Science

Today’s Lesson: Properties of Water

Water is a Polar Molecule

Water molecules are polar.Polar = has a positive side and a negative side.

The negative part of a water molecule is attracted to the positive part of another.

Water Forms Hydrogen BondsThe bonds formed between water molecules are called hydrogen bonds.

Hydrogen bonds between molecules of water is what causes water’s surface tension

Water’s Boiling and Freezing Points

Water is considered to be so important that the scale we use to measure temperature was set according to water!

Water boils at 100° Celsius Water freezes at 0° Celsius

Frozen water (ice) is less dense than liquid water, which is 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 than 100° Celsius.

Steaming vegetables can be healthier and more delicious because it doesn’t rinse away all the vitamins, and FASTER too because the steam 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 will boil at a lower temperature up at the top of a mountain (=less pressure from atmosphere) than at the 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 hotter than 100° Celsius, because the lid on the pressure cooker 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 the water in a human would boil and turn to steam! NASA says that a person could live about 1 minute in space without a suit.

Note: (don’t need to write in notes) a man accidentally exposed to a vacuum at NASA lost consciousness after about 14 seconds due to lack of oxygen. He said his last memory was “the water beginning to boil on his tongue”. You will NOT explode without a spacesuit in space says NASA.

More about Boiling WaterHow do you know when water is at 100° Celsius when cooking?

When the first bubble of air floats all the way to the top of the water. Do you need to make water boil like crazy for it to be 100° Celsius? No! Just enough for the first bubbles to be rise to the top. After that, it only needs a little heat to stay at 100° Celsius.

What are the bubbles in boiling water made of?

Steam (=water vapor)

Capillary ActionCapillary action occurs when water goes up against the forces of gravity.

Without hydrogen bonds, capillary action could not occur.

Capillary action is how plants and trees transport water from the roots to leaves where photosynthesis occurs.

Capillary Action

Gravity

How Does Capillary Action Occur?1) Adhesion is the attraction between water and other objects.

Example of Water Adhesion

Adhesion allows water to stick to the sides of the tube (can be a straw or inside a plant).

2) Cohesion is water being attracted to itself due to its hydrogen bonds

Adhesion 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 VERY HIGH 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 carbon dioxide (CO2) and forms a weak acid called carbonic acid:CO2 + H2O H2CO3

Carbonic 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 the power to dissolve limestone

Carlsbad Caverns

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?