Acids, Bases & Salts

Chapter 9, Section 1 - Acids, Bases, and pH                                                                                                                             

Acid - A compound that produces hydronium (H3O+) ions when dissolved in water.
  • Acids form H+ ions, which attach to water (H2O) to make hydronium (H3O+).
  • Properties of acids...
    • Taste sour.
    • Cause indicators to change color.
    • Conduct electric current.
    • Are corrosive - can damage material, including skin.

Base - A compound that produces hydroxide (OH-) ions when dissolved in water.
  • Bases either give off OH- ions, or take hydrogen atoms from water to make OH- ions.
    • Metal hydroxides - Bases that contain a metal ion and a hydroxide ion.  (ex. - NaOH)  These are strong bases.
  • Properties of bases...
    • Taste bitter.
    • Feel slippery (like soap).
    • Cause indicators to change color.
    • Conduct electric current.
    • Can damage skin.

Indicator - A compound that changes color, depending on conditions (such as pH).
  • Blue litmus paper turns red in acid.
  • Red litmus paper turns blue in base.
Electrolyte - A substance that conducts electric current when dissolved in water.

Strong Acids & Bases
  • All of the molecules dissolved in water ionize (form ions).
  • Are strong electrolytes - they produce as many ions as the acid/base can possibly form.
  • Metal hydroxides are strong bases.
Weak Acids & Bases
  • Do not ionize completely.
    • Form equilibrium systems (reaction to form ions is reversible).
  • Are weak electrolytes (do not conduct electricity as well as strong acids/bases).

Safety Concerns
  • Concentrated acids/bases can be damaging to the skin.
  • Vapors can harm eyes, mouth and lungs.
  • Precautions...
    • safety goggles, gloves, lab aprons

pH - A value used to express acidity or basicity (alkalinity).
  • The pH scale ranges from 0 to 14.
    • Below 7 is acidic.
    • 7 is neutral.
    • Above 7 is basic.
  • pH is a measure of the concentration of H3O+ ions  =>  related to molarity.
    • The concentration of H3O+ ions in pure water is 1x10-7 M.  The pH is the negative of the power of 10, so 7 in this case.
    • The concentration of H3O+ ions in apple juice is 1x10-3 M.  So, its pH is is 3.
    • Each whole number difference in pH equals a 10x change in acidity/basicity.
    • pH can be measured with pH paper or with electrical pH meters.

    Pg. 300 #1-6, 8-10.

Chapter 9, Section 2 - Reactions of Acids with Bases                                                                                                                

Neutralization Reaction - The reaction of an acid and a base, which produces water and a salt.
  • Strong acid in water...
HCl  +  H2O  =>  H3O+  +  Cl-
  • Strong base in water...
NaOH  =>  Na+  +  OH-

  • Reaction of acid and base ions...
H3O+  +  Cl-  +  Na+  +  OH-  =>  Na+  +  Cl-  +  2H2O

Spectator Ions - Ions that don't change during the reaction.

If the water is removed, the Na+ and Cl- will combine to form NaCl (salt).
Salt - An ionic compound formed when a metal ion replaces the hydrogen in an acid.

If there is...
...more acid than base => solution will be acidic.
...more base than acid => solution will be alkaline (basic).
...the same amount of acid and base => solution will be neutral.

Titration - The process of adding small amounts of one solution to another, in the presence of an indicator, to determine concentration.
Ex. - Bromothymol Blue is yellow in acids, blue in bases.
Start with some acid and bromothylmol blue (yellow solution).
Add base, a little at a time, until the solution changes to blue (at pH 7).

Salts can be almost any combination of cations and anions (except hydroxides and oxides - which are bases).
  • Salts have many uses.
  • Many occur naturally, some are made by chemical reactions.
  • Salts provide ions that are needed by the body...
    • Ca+2 are used in bones and teeth, and allow muscles and nerves to work properly.
    • K+ and Na+ are needed for nerves to function.
    • Cl- balance the positive ions in the body.
    • PO4-3 is used in DNA and transporting energy.
    Pg. 306 #1-7.

Chapter 9, Section 3 - Acids, Bases, and Salts in the Home                                                                                                      

Cleaning Products help water mix with oily substances.
  • Soap - A substance used as a cleaner that dissolves in water.
    • Salts of Na+ or K+.
    • Can dissolve in oil or water.
      • Forms an emulsion that can be rinsed away.
    • Has a polar end (metal ion) and a nonpolar end (fatty acids).
      • Water is attracted to the polar end.
      • Oil is attracted to the nonpolar end.
  • Detergent - A water-soluble cleaner that can emulsify dirt and oil.
    • Salts of Na+ or Kor sometimes NH4+. 
    • Similar to soap, but with a SO3- group at the charged end, instead of a CO2- group.
      • Hard Water - Water with dissolved Mg+2, Ca+2, and Fe+3 ions.
      • Soap combines with ions in hard water to make soap scum (insoluble salt).
      • Detergents don't form soap scum.
  • Ammonia - A weak base.
    • Used in glass cleaners - can remove fingerprints and oily smears.
  • Bleach - A compound used to whiten (remove color).
    • Basic solution of NaOCl (sodium hyopchlorite) - changes substances to colorless forms by releasing oxygen.
      • NEVER add the following to chlorine bleach...
        • ACID - produces chlorine gas, which is deadly.
        • AMMONIA - produces toxic chloramine gas (NH2CL).
    • Bleach is used as a disinfectant (substance that kills harmful bacteria or viruses).
Personal Care & Food Items
  • Healthcare Items
    • Vitamin C = Ascorbic Acid
      • Used for growth and repair.
    • Antacids - Weak bases that neutralize stomach acids.
      • NaHCO3 (sodium hydrogen carbonate = baking soda)
      • Mg(OH)2 (magnesium hydroxide = milk of magnesia)
    • Shampoo
      • Adjusted for pH
        • Higher pH = better at cleaning oils from hair.
        • Lower pH = better at protecting hair.
    • Acid Antioxidants
      • Acids can prevent oxidation by reacting with oxygen before it can react with other molecules.
    • In the Kitchen
      • Acids
        • vinegar & citric acid - used in marinades & to tenderize meat
        • acids help turn milk into yogurt
      • Salts
        • Baking soda (sodium bicarbonate) forms CO2 gas at high temps => used in baking to make bread/cake rise.
      • Bases
        • Drain cleaner (sodium hydroxide) breaks down grease and other things that cause clogs.
    Pg. 313 #1-7.