CHEMISTRY/PHYSICAL SCIENCE
ACIDS, BASES, SALTS
MINI LESSON IV
 
 

VOCABULARY:
  acid
  base
  salt
  hydronium ion
  hydroxide ion
  pH
 litmus paper
 neutralization















1. ACID - a substance that is capable of releasing hydrogen ions (H+) and producing hydronium ions in water solutions (H3O+)

In pure water there is a natural production of H3O+ and OH- ions in equal numbers

When an acid is added to water, the number of hydronium ions dramatically increases.

  HCl  +  H2O  ------->   H3O+                +       Cl-

                                                  acid     water          hydronium ion     chloride ion
 

2. BASE - a substance that produces hydroxide ions, (OH-) in water.

NaOH(aq)   ---------->   Na+(aq)     +   OH-(aq)

                                              sodium hydroxide          sodium ion       hydroxide ion
                                                 (base)















Properties of Acids:

1. sour taste
2. react with metals
3. every acid contains hydrogen
4. almost all acids are formed from nonmetals
5. many are poisonous and corrosive to the skin
 

Common acids - play an important part in daily life.
Examples: vinegar (acetic acid), butter milk (lactic acid), lemons-oranges-grapes (citric acid), stomach acid (hydrochloric acid-aids digestion).

Commercial (industrial) acids
1. sulfuric acid (H2SO4)
2. nitric acid (HNO3)
3. hydrochloric acid (HCl)














Properties of Bases:

1. bases usually taste bitter
2. feel slippery                      NOTE: taste or touch are dangerous ways to test for an acid or base.
3. strong bases are poisonous & corrosive to skin
4. bases break down fats and oils

Common bases - lye, ammonia, milk of magnesia

- the most widely used base is sodium hydroxide (NaOH). Its common name is lye. Sodium hydroxide is used in making soap and to unclog sink drains since it dissolves oil and grease.
- ammonia solution (NH4OH) is used in cleaning compounds
- milk of magnesia (Mg(OH)2) is used as a laxative & antacid
- deodorants contain aluminum hydroxide (Al(OH)3)
 
 












The pH Scale:

The amount of acid a solution contains (its acidity) can be expressed by using the pH scale.

pH - a number that shows acidity; it is a measure of hydronium ion (H3O+) concentration of a solution.

- the pH scale ranges from 0 to 14.
- solutions above 7 are basic (a base)
- solutions below 7 are acidic (an acid)
- a neutral solution is neither acidic or basic (its pH is 7)
- pure water is neutral and has a pH of 7
- strong acids have a pH near 0
- strong bases have a pH near 14
- a low pH means a high hydronium ion (H3O+) amount
- a high pH means a high hydroxide ion (OH-) amount
 
 













Acid-Base Indicators

USE OF INDICATORS:

Acid-base indicators - are used to test for an acid or base, they are usually organic compounds that are different colors in acid or base solutions.

TYPES OF INDICATORS:

a) litmus paper - an indicator commonly used to test for an acid or base.
- Blue litmus paper turns red in an acidic solution.
- Red litmus paper turns blue in a basic solution.
- A neutral solution will not change the color of litmus paper.

b) phenolphthalein - a common acid-base indicator that is colorless in an acid, but turns bright pink in a base.
 
 

NEUTRALIZATION: a chemical reaction in which equal numbers of hydronium ions (from the acid) and hydroxide ions from the base) combine to form water and a salt.

HCl(aq)   + NaOH(aq)   ---------->    NaCl(s)    +     H2O(l)

                                        acid           base                             a salt              water

NOTE: Neutralization explains why bases are used to counter act acids that are spilled on skin or clothing.
a) baking soda is used to neutralize acids
b) antacids (Rolaids) contain bases used to reduce excess stomach acid.














SALTS

Neutralization produces water and a salt.

H2SO4(aq) +       2NaOH(aq)  ---------->  Na2SO4(aq)  + 2H2O(l)

                                     acid                    base                           a salt              water
 

- a salt is a substance which is neither acid or base.
- a salt is formed from the positive ion from a base and the negative ion from an acid.
- most salts contain a metal and a nonmetal

SALT - a compound containing a positive ion from a base and a negative ion from an acid.
Examples: NaCl, Na2SO4, Al(OH)3, CaCO3, etc.