EM

Lesson 14: Properties of Acids and Bases

Acids and Bases

AcidsBases
water soluble are electrolytes taste sourturn blue litmus redneutralize basesreact with metals to make H2(g)react with carbonates to make CO2(g)water soluble are electrolytes taste bitterturn red litmus blueneutralize acidsfeel slippery

Bases:

  • Arrhenius was the first scientist to propose a structure related to acids and bases.
  • He proposed that hydroxide ions (OH-) are responsible for the properties of bases.  Ionic hydroxides (metal ion + OH- ion) are very common bases that separate into their ions when dissolved in water.  This process of separation of ions is called dissociation.

Examples of Bases

sodium hydroxide - NaOH(aq)

NaOH(s) → Na+(aq) + OH-(aq)

calcium hydroxide – Ca(OH)2(aq)

Ca(OH)2(s) → Ca2+(aq) + 2 OH-(aq)  \n

Acids

Arrhenius proposed that the H+ ion is responsible for the properties of acids.    Acids are molecules with a hydrogen attached that can be released in water.  This process of releasing the hydrogen ion is called ionization.

Ionization = the process in which a neutral molecule forms ions.

Examples:  HCl(aq) 🡪 H+(aq) + Cl-(aq)

HC2H3O2 (aq) 🡪 H+(aq) + C2H3O2- (aq)

Strong and Weak Acids and Bases

Hydrochloric acid (HCl(aq)) and acetic acid (HC2H3O2(aq)) are both acids. \n

However, even if we take the same concentration of each acid, hydrochloric is much more corrosive than acetic acid and it conducts electricity better.  It seems to have more acidic properties.  Why is this?

\n Strong Acids

Hydrochloric acid is a strong acid.  Strong acids are acids that ionize 100% in water.

HCl (aq) = H^1+ (aq) + Cl^1- (aq)

Less than half of the HC2H3O2 molecules ionize to make H1+ and C2H3O21-.  Since H1+ ions are the ones that give an acid acidic properties, the end solution is less acidic than a strong acid.

\n Weak acids

Acetic acid is a weak acid.  Weak acids are acids that ionize less than 50% in water.

HC2H3O2 (aq) = H^1+ (aq) + C2H3O2^1- (aq)

Less than half of the HC2H3O2 molecules ionize to make H1+ and C2H3O21-.  Since H1+ ions are the ones that give an acid acidic properties, the end solution is less acidic than a strong acid.

Properties of Equal Concentrations of Strong and Weak Acids

Weak AcidStrong Acid
conducts electricity lessreacts more slowly with metalhigher pHless corrosiveconducts electricity morereacts more quickly with metallower pHmore corrosive

Summary

  1. Strong acids ionized 100% and are more “active”; Weak acids ionize less than 100% and are less “active”
  2. OH- indicates bases; H+ indicate acids
  3. Ionization - going from a neutral molecule to charged ions; dissociation - the “splitting apart” process