Chemistry Notes: Acids and Bases

Properties of Acids and Bases

Acids taste sour (vinegar,

lemons) aqueous solutions of acids

are electrolytes cause indicators to change

colors many metals react with

acids to produce H2 gas react with bases to form a

salt and water most formulas begin with

H

Bases bitter taste (soap,

unsweetened chocolate) bases are electrolytes in

aqueous solution cause indicators to

change colors feel slippery react with acids to form a

salt and water often contain OH- , or

ammonia NH3

ExamplesThe bolded formulas below to STRONG acids and

bases

Common acids HCl HNO3

H2SO4

H3PO4

HC2H3O2

H2CO3

Common bases NaOH KOH Ca(OH)2

LiOH NH3

The pH of a substance can tell us if it’s an acid, a base, or neutral. pH is a measurement of the concentration of hydrogen ions (H+) in a solution. The more hydrogen ions present, the more acidic a substance is.

Acids have large amounts of hydrogen ions, and low pH (pH < 7).

Bases have small amounts of hydrogen ions, and high pH (pH > 7).

Measuring pH

Another measurement, pOH, tells use the concentration of hydroxide (OH-) ions in a solution. The more hydroxide ions present, the more basic a substance is.

Acids have small amounts of hydroxide ions, and high pOH (pOH > 7).

Bases have large amounts of hydroxide ions, and low pOH (pOH < 7).

Neutral substances have equal amounts of hydrogen and hydrogen ions (pH = 7, pOH = 7).

The pH and pOH of a substance always add up to 14.

 pH = 5.6 NH3

 Large concentration of OH- ions   Small concentration of H+ ions

pOH = 3.2 pH = pOH H2SO4 NaOH

 Large concentration of H+ ions HCl

Practice: Are these solutions acidic, basic, or neutral?

If the pH of a solution is 6, what is its pOH? Is it an acid or base? 

If the pH of a solution is 4, what is its pOH? Is it an acid or base? 

If the pOH of a solution is 3, what is its pH? Is it an acid or base?

Practice: Are these solutions acidic, basic, or neutral?

Indicators are substances that change color in solutions of different pH

Help determine approximate pH

Indicators

Colorless in acid

Pink in base

Phenolphthalein

Mixture of indicators Changes into

different colors at each pH (rainbow)

Red/orange in acid, blue/purple in base, green around pH = 7

Universal indicator

Blue litmus turns red in acid

Red litmus turns blue in base

Litmus paper