Acids & Bases

Properties  electrolytes  turn litmus red  sour taste  react with metals to form H 2 gas  slippery feel  turn litmus blue  bitter taste  vinegar, soda, apples, citrus fruits  ammonia, lye, antacid, baking soda

Acid and Bases

Svante Arrhenius ( )

Arrhenius Acids  Arrhenius - In aqueous solution… HCl + H 2 O  H 3 O + + Cl – AcidsAcids form hydrogen ions (H + ) [hydronium ions (H 3 O + )] H HHHH H Cl OO – + acid

Acids -- Example  Hydrochloric Acid Forms Hydrogen Ions (H+) in solution Forms Chloride ions (Cl-) in solution/ water hydrogen ions (H + ) = [hydronium ions (H 3 O + )] = proton

Monoprotic acidsDiprotic acidsTriprotic acids HCl HC2H3O2HC2H3O2 HNO 3 H 2 SO 4 H 2 CO 3 H 3 PO 4 Acids - an acid with more than one H +  Polyprotic - an acid with more than one H +

Arrhenius Bases  Arrhenius - In aqueous solution… BasesBases form hydroxide ions (OH - ) NaOH + H 2 O  Na + + OH -

Some Common Bases NaOHsodium hydroxide lye KOHpotassium hydroxideliquid soap Ba(OH) 2 barium hydroxide stabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) Al(OH) 3 aluminum hydroxideMaalox (antacid)

Copyright Pearson Prentice Hall Acids, Bases, and pH The pH scale Chemists devised a measurement system called the pH scale to indicate the concentration of H + ions in solution. The pH scale ranges from 0 to 14.

pH Scale pH of Common Substances

pH = -log[H + ] pH Scale 0 7 INCREASING ACIDITY NEUTRAL INCREASING BASICITY 14 pouvoir hydrogène (Fr.) “hydrogen power”

pH Scale = Concentration of H+/ hydrogen ions Power of hydrogen pH = -log[H + ] Concentration Of hydrogen ion ( H+) Concentration is the amount of a substance (e.g. H+) per unit volume

pH Scale  What is the pH of HNO 3 with a [H+] concentration of M ? pH = -log[H + ] pH = -log[0.050] pH = 1.3 Acidic or basic? Acidic

Strong vs. Weak Acids  Strong Acids: ionize completely in aqueous solutions Hydrochloric acid (HCl) Nitric acid (HNO 3 ) Sulfuric acid (H 2 SO 4 )  Weak Acids: ionize only slightly in aqueous solutions Acetic acid (HC 2 H 3 O 2 )

Strong vs. Weak Acids

Strong vs. Weak Acid Protons are hydrogen ions (H+) Negative ions– Non- metal anion

H + = hydrogen ion A - = any acid anion Strong vs. Weak Acid HA H + + A - H2OH2O  

Strong vs. Weak Acids H + = hydrogen ion A - = any acid anion

Strong vs. Weak Bases  Strong Bases: ionize completely into metal cations and hydroxide ions Sodium Hydroxide (NaOH) Calcium Hydroxide (Ca(OH) 2 ) Magnesium Hydroxide (Mg(OH) 2 )  Weak Bases: react with water to form hydroxide ions Ammonia (NH 3 ) Not very soluble

Strong Bases  Strong Bases will completely ionize (break into ions) in water.  Sodium ion (Na+)  Hydroxide ion (OH-)

Weak bases  Weak bases only partial ionize in water  For example, only some ammonia (NH 3 ) becomes ammonium ion (NH 4 + ) and only some water (H 2 0) become hydroxide ion (OH - )

Concentration vs. Strength  Concentrated/Dilute = indicate how much of an acid or base is dissolved in solution  Strong/Weak = indicates how many molecules ionizes or dissociates  Is it possible to have a strong base that is only mildly basic? How?

Concentrated vs. Dilute