Properties of Water 8/27/2015 Objective: SWBAT observe the properties of water and apply to real world scenarios

How to take notes from this powerpoint: If something is bolded and underlined, write it down. Draw applicable pictures (as instructed/needed)

Draw a water molecule Label the bonds H to O: Covalent bond Electrons (have what charge?) hang out closer to the O than to the H which makes water POLAR

Think about the following question:

What does it mean to be “polar”?

POLAR: the two ends have different charges Charged regions are attracted to the OPPOSITE charged parts of other waters. (So the neg end of one water is attracted to the pos end of another)

Like this: (You may want to sketch this in your notes)

HYDROGEN BONDS: Hold DIFFERENT water molecules together (What hold each water molecule to itself?) Each water molecule can make up to 4 hydrogen bonds. WEAK (1/20 of a covalent bond) THIS IS WHAT MAKES WATER SO AMAZING! Check for understanding: Why is it unlikely that two neighboring water molecules would arrange themselves like this:

Start a list in your notes Start a list in your notes. The heading is “4 Emergent Properties of Water” Remember, don’t write every word on the slide, just the bolded and underlined ones.

1. COHESION Water sticks to itself Ex: Water evaporating from the leaves pulls water up from the roots Fig 3.3 on pg 47 of the textbook Adhesion: water sticks to other stuff

Make a note to your self to “See fig 3 Make a note to your self to “See fig 3.3 on pg 47” so you remember to get a good look at that picture

Cohesion and surface tension Watch this cool video: https://www.youtube.com/watch?v=RphuMEUY3Og (This website is also on the course website) Surface tension: how hard it is to break the surface of a liquid TRY IT: Slightly overfill a glass of water. What do you think will happen?

Be ready for the SECOND emergent property of water!

2. Moderates Temperature Specific heat: amount of heat absorbed to raise 1ºC (Jot the following in your notebook) Predict: what will happen to the balloon filled with AIR? Observe: Predict: what will happen to the balloon filled with WATER? Explain what happened on the macro and micro level. (Reference your picture of water!) (Air balloon with pop, the water balloon will not. Water has a high specific heat which prevents the balloon from changing temperature, because the water is absorbing the heat without changing temperature drastically. This occurs because of water’s bent polar configuration which leads to hydrogen bonding. Hydrogen bonds lead to the cohesion of water molecules to one another; it takes a high amount of energy to break these bonds.)

What are the implications? High specific heat Water can absorb a lot of heat before it evaporates Evaporative cooling Which evaporates faster, water or alcohol? Why? Have to break all those H bonds before you can evaporate What’s an example of evaporative cooling? Do alcohol/water demo

Here comes the THIRD Property!

3. Freezing expansion Water expands as it freezes, so it can ________________ THIS IS SO WEIRD because most liquids ______________ Implications: “If the ice sank, then eventually all ponds, lakes, etc would freeze solid. Only the top [centimeters] would thaw in the summer. Instead, the floating ice INSULATES the liquid water below, allowing life to exist under the frozen surface.” –adapted from the textbook, pg 50 FLOAT/SINK

Last one! Here comes #4…

4: Versatile solvent A solvent is a substance that dissolves, or breaks apart, another substance (known as a solute). Generally: like dissolves like (polar dissolves polar, nonpolar-nonpolar) Oil + alcohol Oil + water

EXIT TICKET: Why is this funny? (Explain the science of the joke on the back of the DN) What property of water is being described here? What does it mean to be polar?

PRE-LAB HOMEWORK Homework: read the lab procedure Answer the following questions: From the handout # 1, 2, 3, 6 on page 68-70