The Chemistry of Life Water: Acids, Basis, & pH copyright cmassengale
Acids and Bases One of the most important aspects of a living system is the degree of acidity or alkalinity
–A water molecule is neutral, but can react to form hydrogen and hydroxide ions. –Water disassociates (ionizes) in itself. –Breaking apart of the water molecule into two ions of opposite charge (due to strong attraction of oxygen atom of one molecule for H atom of another water molecule) –Usually does this for 1/10,000,000 or 1E -7 H 2 O H + (hydrogen ion) + OH - (hydroxide ion) H + + H 2 O H 3 O (hydronium ion) Water Dissociation
1 water molecule in 550 million naturally dissociates into a Hydrogen Ion and a Hydroxide Ion1 water molecule in 550 million naturally dissociates into a Hydrogen Ion and a Hydroxide Ion Hydrogen Ion Hydroxide Ion Acid Base Acid Base H 2 O H + + OH - copyright cmassengale
The pH Scale Water dissociation is the basis for this scale pH is a measure of this dissociation. According to the following formula: pH = -Log [H + ] logarithmic scale for comparing the relative concentrations of hydronium ions and hydroxide ions in a solution Each pH unit represents a factor of 10X change in concentration copyright cmassengale How much stronger is a pH3 than a pH of 5?
The pH Scale Indicates the concentration of H + ions Ranges from 0 – 14 pH of 7 is neutral pH 0 up to 7 higher acidity … H + > OH - pH above 7 to 14 higher alkalinity… OH - > H + copyright cmassengale Concentration
The pH Scale At a pH of 7, the concentration of H + ions and OH - ions is equal. copyright cmassengale
Acids Strong Acid = pH 1-3 High in H + ions Lower number of OH- ions copyright cmassengale
Acids An acid is any compound that forms H + ions in solution (Simple definition) Number of hydronium ions in solutions is greater than the number of hydroxide ions HCl H + + Cl - copyright cmassengale
Acids Facts Sour taste Affect the color of indicators: turn litmus paper from blue to red pH 1-6.9 common acids: sulfuric, hydrochloric, nitric, and acetic acids
Bases Strong Base = pH 11 – 14 High in OH - ions Lower in number of H+ ions copyright cmassengale
Bases A base is a compound that produces hydroxide ions (OH - ions) in solution. Number of hydroxide ions in solution is greater than the number of hydronium ions NaOH Na + + OH - copyright cmassengale
Bases Facts Bases are slippery Bitter taste Turn litmus paper from red to blue pH 7.1-14 potassium hydroxide, calcium hydroxide, sodium hydroxide, and ammonium hydroxide
the lower the pH the stronger the acid the higher the pH the stronger the base pH 7.0 is neutral REMEMBER!!
Salt Salt is a compound formed when an acid is mixed with a base (positive ion from a base and a negative ion from an acid)
Neutralization A neutralization reaction occurs when an acid and a base combine to form salt and water
Precipitate A precipitate is an insoluble substance crystallizes out of solution (ex: salt from a neutralization reaction)
Precipitation reaction The process of forming a precipitate is precipitation
Buffers The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5. Controlling pH is important for maintaining homeostasis. Remember one example we already learned about of something in biology that needs specific pH to work?
Buffers copyright cmassengale Control of pH is very important Most enzymes function only within a very narrow pH Control is accomplished with buffers made by the body Buffers keep a neutral pH (pH 7)
Buffers Weak acids or bases that react with strong acids or basesWeak acids or bases that react with strong acids or bases Made by the bodyMade by the body Prevent sharp, sudden changes in pH (keep pH neutral)Prevent sharp, sudden changes in pH (keep pH neutral) Weak Acid Weak Base copyright cmassengale
Buffers Buffers neutralize small amounts of either an acid or base added to a solution Complex buffering systems maintain the pH values of your body’s many fluids at normal and safe levels
Buffers copyright cmassengale Buffers resist changes to the pH of a solution when H + or OH - is added to the solution. Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted.
Some Key Points for the Test Many properties of water are emergent properties due to hydrogen bonding. The cohesion of water molecules to each other is exploited by plants and animals. Water resists temperature changes by absorbing lots of heat. Lower density of ice causes it to float & insulate the water below. The polarity of water allows it to dissolve other polar molecules. Non-polar compounds are hydrophobic and not easily dissolved in water. Adding or removing hydrogen ions changes the pH of a solution. Buffers resist pH changes by accepting or donating H ions when [H+] changes. copyright cmassengale