H2O 2.2 Properties of Water # of Protons 10 10 # of Electrons 18 Atomic Mass

The Water Molecule Slightly Positive (+) Electrons hang out more often near the oxygen atom. Covalent bonds between oxygen and hydrogen. Slightly Negative (-) Polarity – water is polar because of an uneven distribution of electrons between oxygen and hydrogen.

Hydrogen Bonds Because of their partial charges water molecules become attracted to each other by weak hydrogen bonds Hydrogen bonds are not as strong as ionic or covalent bonds Cohesion – attraction between molecules of the same substance Adhesion - attraction between molecules of different substances.

COHESION ADHESION Water compounds attract Water compounds attract To one another- causes water to “bead” Water compounds attract To glass molecules And form a meniscus

Capillary Action Def – water climbing up a small tube because of the adhesion to the sides and the cohesion between water molecules.

Other Unique Properties of Water High specific heat - water will absorb lots of heat energy with a minimal temperature increase High heat of vaporization – water will absorb lots of heat energy with minimal evaporation.

Other Unique Properties of Water Expansion on freezing – water forms a crystalline structure that expands and is less dense than its liquid state

Other Unique Properties of Water High surface tension – hydrogen bonds hold water together tightly, so the waters surface acts like a membrane

Solutions and Suspensions Mixture – a material that consists of 2 or more elements or compounds physically mixed together but are not chemically combined.

Solutions All the components of a solution are evenly distributed throughout the solution. Solute – the substance being dissolved (salt) Solvent – the substance in which the solute is dissolved. (water) Water is the universal solvent! (Polar molecules dissolve polar molecules) Animation

Acids and Bases Animation Acidity and Alkalinity is measured by the concentration of . . . Hydrogen Ions H+ Hydroxide Ions OH-

Acids Bases Neutral Solution Produce H+ ions in solution If H+ > OH- then the solution is acidic. Bases Produce OH- ions in solution If OH- > H+ then the solution is basic Neutral Solution If OH- = H+ then the solution is neutral

Measuring Acidity or Alkalinity pH Scale: (power of Hydrogen) as in Hydrogen ions

Use the structure of a water molecule to explain why it is polar. Why is water such a good solvent? What is the difference between a solution and a suspension? How do hydrogen bonds between water molecules occur? How does the body counteract a drop in blood pH during strenuous exercise? If a strong acid is dissolved in pure water will the pH of the solution be greater or less than 7?

Water Chemistry Please draw the structure of a water molecule (H2O). Label the charges on the molecule that make it polar (negative and positive ends). See if you can connect the water molecule that you drew to two other molecules of water using hydrogen bonds. Can you think of any unique properties that water displays?

Water Chemistry Explain why water is “polar” in your own words. Explain capillary action in your own words. Explain surface tension in your own words.

1. pH = the negative logarithm of the hydrogen ion (H+) concentration. 2. pH of water = 1x10-7 or 7 Try this: pH .000000001 = ? Or pH .001 = ? 3. For each change of a pH unit the concentration of H+ ions differs by 10 times. Try this: How many times more acidic is pH 2 compared to pH 5?

pH Laboratory Shampoo Lemon juice Drain cleaner Milk Bleach Soda (pop if you’re from Pittsburgh) Water

Soda (pop if you’re from Pittsburgh) (3) Water (7) pH Laboratory Shampoo (5-7) Lemon juice (2) Drain cleaner (14) Milk (7) Bleach (12) Soda (pop if you’re from Pittsburgh) (3) Water (7) LITMUS PAPER: Blue turns Red = Acid Red turns Blue = Base

According to the scale, what substance is neutral? What solution has an [H+] of 0.01? Which substance produces the most OH- ions in solution? How many more times basic is pH 14 compared to pH 11. What substance has a hydrogen ion concentration of 1 X 10-4

Water Molecule

Properties of Water Quiz Questions Use the Finish line Water Chemistry section to develop 3 good questions about water. Two of them should be multiple choice and 1 should be a short answer question. Submit for credit, you might see them on the next quiz!