Pick Up Unit 2 Exam For Item Analysis

CNN Headline 3/10/04 Rawlins WY: 300 Elk found dead in pasture. No visible

signs of trauma or injury. Scientists baffled.

The Cause of Death

• Rhabdomyelitis• Breakdown of skeletal

muscle tissue due to buildup of lactic acid

• Symptoms include weakness, disorientation and red urine

3/30/04: The Killer Is Found

• Xanthoparmelia chlorochroa (lichen)

• Healthy elk fed Xanthoparmelia chlorochroa quickly developed rhabdomyelitis

• Southern elk lack intestinal microbes that break down toxins

pH Scale

• What is it?– A measurement of the relative concentration

of hydronium and hydroxide ions produced when a substance disassociates in water

– The pH scale is an inverse logarithmic scale of the concentration of the hydronium ions

What is an inverse logarithmic scale and how does this relate to pH?

• The “rank” on the scale refers to the absolute value of the exponent

• In an inverse scale, the lower the ranking, the higher the amount

• In measuring pH, the exponents are negative, so a larger number is a smaller concentration

1 Change in pH Rank = Factor of 10!pH Conc. H+ Example  

0 10,000,000 Battery acid Most acidic

1 1,000,000 Hydrochloric acid  

2 100,000 Lemon juice  

3 10,000 Orange juice  

4 1,000 Acid rain  

5 100 Black coffee  

6 10 Saliva  

7 1 Distilled water Neutral

8 0.1 Salt water  

9 0.01 Baking soda  

10 0.001 Milk of magnesia  

11 0.0001 Ammonia solution  

12 0.00001 Soapy water  

13 0.000001 Oven cleaner  

14 0.0000001 Liquid drain cleaner Most alkaline

HYDRONIUM v. HYDROXIDE

• A hydronium ion is a hydrogen ion (H+) that becomes attached to a water molecule

• A hydroxide ion is a negatively charged diatomic (2 atom) ion containing an oxygen and hydrogen atom (OH-)

Disassociation of Water• Water theoretically disassociates into equal

concentrations of hydronium and hydroxide ions• 1 liter of water should disassociate into 1x10-7

hydronium ions and 1x10-7 hydroxide ions• This is why water has a pH of “7”

Does Everything Have A pH?

• pH is ONLY the measure of the hydronium ion concentration.

• Substances that do not disassociate do NOT have a pH!

• For substances that disassociate in water, the sum of the exponents for hydronium and hydroxide ions is always -14

WHAT MAKES A SUBSTANCE NEUTRAL, ACIDIC or BASIC?

ACIDS DEFINED

• If the concentration of hydronium ions is greater than the conc. Of hydroxide ions, the substance is an ACID

• Example: Substance disassociates into 1x10-3 mol/L H30 ions and 1x10-11 mol/L OH- ions

DIFFERENT ACIDS

• Hydrochloric Acid (HCl) = produces 1 H+ ion in solution

• Sulfuric Acid (H2SO4) = produces 2 H+ ions in solution

• Phosphoric Acid (H3PO4) = produces 3 H+ ions in solution

PROPERTIES OF ACIDS

• Sour taste• Pungeant odor• Burning sensation

when in contact w/epithelium (skin)

BASES DEFINED

• If the concentration of hydroxide ions is greater than the conc. Of hydronium ions, the substance is a BASE

• Example: Substance disassociates into 1x10-8 mol/L H30 ions and 1x10-6 mol/L OH- ions

DIFFERENT BASES

• Sodium Hydroxide (NaOH) = produces 1 OH- ion in solution

• Magnesium Hydroxide (MgOH2) = produces 2 OH- ions in solution

• Aluminum Hydroxide (AlOH3) = produces 3 OH- ions in solution

PROPERTIES OF BASES

• Bitter taste• Slippery texture• Bases also “burn” on

contact with skin and smell pungeant

NEUTRALIZATION

• When equal concentrations of hydronium and hydroxide ions are brought together (i.e. acids and bases of equal strength and concentration), the substances disassociate and reassemble into an inorganic salt and water.

Neutralization (example)

• 1M HCl and 1M NaOH are brought together, 1 H3O ion and 1 OH- ion are disassociated.

• The H3O and OH- ion join to form HOH

• The Na+ cation and Cl- anion bond to form salt

Will a volume of 1M H2SO4 be neutralized by an equal volume of

1M Al(OH)3 ? Why or why not?

Why are pH and neutralization biologically significant?

Homeostatic Connections To pH• Carbon dioxide sensors

in carotid artery measure blood pH and tell brain when to signal lungs to breathe

• Absorption and digestion require specific pH

• pH may prohibit parasitic infections

• Changes in pH may alter or destroy enzymes

How Do Humans Maintain pH?• Body is slightly

alkaline, but ranges from pH 2 to pH 11 in matter of centimeters

• Acid substances are not always acidic when they are absorbed

• BUFFERS resist changes in pH