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! pHConc. H + Example 010,000,000Battery acidMost acidic 11,000,000Hydrochloric acid 2100,000Lemon juice 310,000Orange juice 41,000Acid rain 5100Black coffee 610Saliva 71Distilled waterNeutral 80.1Salt water 90.01Baking soda Milk of magnesia Ammonia solution Soapy water Oven cleaner Liquid drain cleanerMost 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 H 3 0 ions and 1x mol/L OH - ions

DIFFERENT ACIDS Hydrochloric Acid (HCl) = produces 1 H + ion in solution Sulfuric Acid (H 2 SO 4 ) = produces 2 H + ions in solution Phosphoric Acid (H 3 PO 4 ) = 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 H 3 0 ions and 1x10 -6 mol/L OH - ions

DIFFERENT BASES Sodium Hydroxide (NaOH) = produces 1 OH- ion in solution Magnesium Hydroxide (MgOH 2 ) = produces 2 OH- ions in solution Aluminum Hydroxide (AlOH 3 ) = 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 H 3 O ion and 1 OH - ion are disassociated. The H 3 O 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