Water

• essential for life (as we know it!)• any other chemical with this low of a

molecular weight = GAS (but it’s a liquid at room temp!)

• b/c of it’s polarity, it tends to stick to itselfCOHESION

b/c of it’s polarity, it tends to stick to other stuffADHESION

Temperature

• b/c H2O molecules are so strongly attracted to each other, it requires quite a bit of heat to disrupt those bonds

• H2O can absorb a lot of heat and the temperature doesn’t change too much

• converse is true as well• moderates temperature on land• moderates temperature in your body

– sweating fever

Cohesion• b/c of H+ bonds, H20 has a HIGH surface

tension– water striders

Adhesion

• b/c of H+ bonds, H20 has a HIGH surface tension– meniscus in glass containers

http://www.chemistryland.com/CHM151W/04-Solutions/liquids/meniscus.jpg

States of Matter

• solid: electrons moving slowly • liquid: electrons moving faster• gas: electrons moving FAST!!

• usually when a substance solidifies, it shrinks: the atoms move more closely together

• NOT H2O: expands b/c H bonds form rigid structure holding each molecule apart

so?

• b/c of this, solid H2O (aka. ice) is less dense than liquid H2O

• so?• floats on top of body of water

(prevents them from freezing solid-insulation)

• pop can explodes in freezer (you’re in trouble now!)

Like dissolves Like

• polar substances dissolve in polar solventsmeans they get shells of hydration!

• Solution = solute + solution– in us, solution = H2O

• non-polar substances DO NOT dissolve in polar solvents

Forms shells of hydration!

http://web.virginia.edu/Heidi/chapter2/chp2.htm

pH

• water is constantly moving; a certain percentage of those molecules break up– ions are formed:

• H+

• OH-

– have equal amounts of each type of ion• some compounds release only H+ • some compounds release only ions that can

accept H+ (negatively charged)

pH

• ACID: compound that releases H+

– strong: throw it in H2O and it dissolves completely

– weak: throw it in H2O, some dissolves, some doesn’t

• BASE: compound that accepts H+

– strong: throw it in H2O and it dissolves completely

– weak: throw it in H2O, some dissolves, some doesn’t

• p = -log of• H = hydrogen

pH

• pH scale tells you number of H+ ions present• pH = 0 (pure H+)• pH = 1 (10 x fewer H+)• pH = 2 (10 x fewer H+)

• b/c pH = -log, you get stronger (more H+ ions) as the number gets lower

Figure 2.14_1

Incr

easi

ngly

ACI

DIC

(Hig

her H

con

cent

ratio

n)Tomato juice

pH scale

Battery acid

Lemon juice,gastric juice

Vinegar, cola

NEUTRAL[H][OH]

Rainwater

Human urine

Saliva

Pure water

pH

• pH gets higher = fewer and fewer H+

• so pH of 14 = safe, right?– NO!!

• 7 is neutral: = number of H+ and ion that can accept H+

• as you go up the scale, the amount of ions that can accept H+ increases (becomes basic or alkaline) (10 x diff. between each #)

Figure 2.14_2

Oven cleaner

Incr

easi

ngly

BAS

IC(H

ighe

r OH

con

cent

ratio

n)

NEUTRAL[H][OH]

Household bleach

Household ammonia

Milk of magnesia

Pure water

Human blood,tears

Seawater

pH scale

Figure 2.14_3

Acidicsolution

Neutralsolution

Basicsolution

Buffer: minimizes Δs in pH

• buffers accept H+ when it is high• buffers donate H+ when it is low

• keeps pH in a stable position• buffers in your blood keep you from dying

when your body produces a lot of acids