Lecture Notes - Strong Acids and Bases Std 5b

 

 

Strong acids or bases are those that completely dissociate. This means the cations and anions of 100% of the acid or base molecules separate into ions.

 

Strong acids & bases to memorize

ACIDS pH 0-6

BASES ph 8 - 14

HCl (hydrochloric acid)

NaOH (sodium hydroxide)

H2SO4 (sulfuric acid)

KOH (potassium hydroxide)

HNO3 (nitric acid)

LiOH (lithium hydroxide)

HBr (hydrobromic acid)

RbOH (rubidium hydroxide)

HClO4 (perchloric acid)

CsOH (cesium hydroxide)

 

 

Examples of ionization

 

NaOH(s) is a strong base when dissolved in water. When dissolved in water you no longer have NaOH(s) as a molecule.

 

NaOH(s) + H2O (l) ----> Na+ (aq) + OH- (aq) + H2O (l)

 

If we put 1,000,000 NaOH molecules in water, we will get 1,000,000 Na+ and 1,000,000 Cl- and no NaOH (s) molecules.

 

HCl(g) is a strong acid only when it is dissolved in water.

 

HCl(g) + H2O (l) ----> H+(aq) + Cl-(aq) + H2O (l)

 

As with the NaOH, the HCl as a gas is bubbled into water. It dissolves in the water and is no longer HCl (g). So, if we put 1,000,000 HCl (g) molecules into the water, we will have 1,000,000 H+(aq) ions and 1,000,000 Cl-(aq) ions and no HCl (g) molecules in the water.

 

FACTS & History

 

acids taste sour, and form ions ( H+ )

Examples (weak acids):

vinegar (HC2H3O2), citrus fruits (oranges, tangerines, grapefruit, lemons all have citric acid) , apples (maelic acid)

Examples (strong acids):

HCl (hydrochloric acid), HNO3 (nitric acid)

 

bases feel slippery (like soap) and taste bitter, and form ions ( OH- )

Examples (strong bases):

NaOH and all alkali metals (Group 1) in combination with OH- ions.

 

Acid-Base indicators

phenolphthalein put a few drops in water, if base is present (OH- ions) it will turn purple, but it is clear in neutral and acid solutions

litmus paper turns red is solutions is acid and blue is solution is basic .

universal paper has a different color of every pH .

 

Svante Arrhenius (Sweden) - Acids known since 1300. Found that acids are conductive (they will light our light bulb we use for conductivity tests). Found that strong acids act like strong electrolytes (ions). He said that acids must ionize. He said that acids must produce H+ ions.