Water Very unique properties make this the most important molecule to life on Earth.

Review… Water is polar… what does this mean? Which is more electronegative, oxygen or hydrogen? Draw a water molecule and label the positive and negative ends of the molecule.

The polarity of water leads to… Hydrogen bonding- attractive force between polar molecules. Occurs between the hydrogen of one molecule and another atom in a different molecule

Water is the solvent for life. Molecules that are IONICALLY bonded and other POLAR molecules dissolve in water Nonpolar substances that have no affinity for electrons do not dissolve in water.

Cohesion Through cohesion, water sticks to water (thanks to hydrogen bonds) Cohesion helps plants transport water through vessels

Adhesion Through adhesion, water sticks to other molecules (like the side of a glass) Adhesion also helps keep water moving up against gravity in plants.

Surface Tension Related to cohesion Surface tension is when molecules resist being pulled apart due to strong hydrogen bonds… form a “film”.

Specific heat Large amounts of energy are needed to change the temperature of water. Example- pools Evaporative cooling

Density Why can’t you fill a water bottle completely when you want to freeze it? What occurs to the structure of water when it freezes? It expands. Insulation for life below the surface…

Lab- Properties of Water You and your group will rotate through 4 activities at different stations. Please WAIT for Ms. Barlow to tell you when to rotate. Changes: When the lab says to use ethanol, we are using isopropyl alcohol. At Station 4, don’t worry about measuring out amounts. Just sprinkle a bit in or add a few drops. Also make sure you add to the water beaker, don’t add water to the smaller beakers. Remember, each station has materials for class use. Your area needs to be cleaned and straightened for the next group.

Exit Slip Choose 4 of the words on the vocab packet you either don’t know or only sort of know. Fill in a Frayer model for each word:

Inquiry Lab- What affects the number of water drops that fit on a penny? Your group will decide on a testable question to conduct on inquiry lab to test one factor that affects how many water drops fit on a penny. Today, as a group: Decide on your testable question. Identify your IV, DV, control (if applicable), and constants. List your materials needed. Write your hypothesis Have an idea about your procedure Next class, you will conduct the experiment in order to finish the lab report.

Bellringer Practice sheet about water and hydrogen bonds

Acids Certain molecules, ionic and covalent, dissociate in such a way that they release a hydrogen (H+) ion. These substances are called acids.  Since a hydrogen ion is really just a single proton in most cases, the chemist’s definition of an acid is a “proton donor.”

Acids If very many protons (hydrogen ions) are “donated” the effect can be very profound, such as burning your skin or dissolving metal.  One acid is hydrochloric acid.  Since nearly all of it is dissociated in water, it is called a strong acid.  Acids that do not dissociate completely are called weak acids. Other examples: citrus fruits, stomach acid, apple juice

Bases The opposite of an acid is a base. The measure of how acidic or basic a substance is known as pH. The most common bases produce hydroxide ions (OH-).

Bases A typical strong base is sodium hydroxide, the principal component of lye.  Sodium hydroxide dissociates to form a sodium ion and a hydroxide ion. A strong base can give your skin a much worse burn than an acid. Other examples: soaps, cleaning solutions

Acid + Base =? When a base and an acid are mixed, the hydroxide ion from the base combines with the hydrogen ion from the acid to form water.   This process is called neutralization.

The pH Scale- ranges from 0-14 The pH scale measures how acidic or basic a substance is. It ranges from 0-14. 0-6.9 is acidic. A pH of 1 means lots of hydrogen ions and VERY ACIDIC pH of 14 means lots of hydroxide ions (or low H+) and VERY BASIC A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic.

The pH scale is logarithmic. For example, a pH of 4 is 10 times more acidic than a pH of 5 and 100 times more acidic than a pH of 6. Practice: How much more acidic is a pH of 1 than a pH of 4? How much more basic is a pH of 10 than a pH of 9?

Most organisms… need to keep their pH in a VERY narrow range(around 7). Some plants do thrive on acidic soil but again, the range must be kept very controlled. Buffers: Compounds that bind to H+ when the H+ concentration gets too high (too acidic) Our blood has to stay at 7.35 – 7.45 so it is slightly basic. Any change for more than a couple of hours will kill you… We have buffers in our blood that prevent any changes

Buffer

Vocab Packet Choose 4 of the words on the vocab packet you either don’t know or only sort of know. Fill in a Frayer model for each word: (*You should have 12 words completed by now if you are on track!)

Make Up Time If you need to make up a lab (microscope, exercise, water, etc), this is a great time to get that done. If you are behind on notes, you can get those during this time. If you are behind on the vocab packet, you may catch up during this time. If you have missed a quiz, you may take that during this time. This is not social time. How well you use this time will determine if any future make up time will be given in class.