Acids and Bases I Dr. Ron Rusay Summer 2004 © Copyright 2004 R.J. Rusay

Introduction to Aqueous Acids  Acids: taste sour and cause certain dyes to change color.

Introduction to Aqueous Bases  Bases: taste bitter, feel soapy and cause certain dyes to turn color.

Electrolytes  Aqueous solutions can be categorized into 3 types: non-electrolytes, strong electrolytes or weak electrolytes based on their ability to conduct electricity.  A solution must have ions to conduct.  Pure Water does not conduct.  Aqueous solutions can be tested for conductivity which will determine the degree of ionization of the solutes.  It is possible to have full or partial ionization. © Copyright R.J. Rusay

Solution Test Apparatus for Electrolytes

Conductivity

Electrolytes / Ionization

Electrolytes  Almost all ionic compounds and a few molecular compounds are strong electrolytes.  Several molecular compounds are weak conductors, most are non-conductors.  Conductivity is directly related to the amount of ionization, i.e. ions in solution. Table salt, sodium chloride, is completely ionized: NaCl (s) + H 2 O (l) ---> NaCl (aq) ---> 0.10molNa + (aq) + Cl - (aq) © Copyright R.J. Rusay

Strong vs. Weak Electrolytes

Models of Acids and Bases  Arrhenius Concept: Acids produce H + in solution, bases produce OH  ion.  Brønsted-Lowry: Acids are H + donors, bases are proton acceptors. HCl + H 2 O  Cl  + H 3 O +

Lewis Acids and Bases  Lewis Acid: electron pair acceptor  Lewis Base: electron pair donor

Conjugate Acid/Base Pairs HA(aq) + H 2 O(l)  H 3 O + (aq) + A  (aq) conj conj conj conj  conjugate base: everything that remains of the acid molecule after a proton is lost.  conjugate acid: formed when the proton is transferred to the base.

Conjugate Acid/Base Pairs  conjugate base: everything that remains of the acid molecule after a proton is lost.  conjugate acid: formed when the proton is transferred to the base.

Acid Strength  100% of the acid is ionized. For example nitric acid, HNO 3. Other common strong acids are _______ and ___________.  100% of the acid is ionized. For example nitric acid, HNO 3, produces 100% H + (aq). Other common strong acids are _______ and ___________.  Stong acids produce very weak _________________, eg. (NO 3  ) Strong Acids:

Structure and Acid Strength  Bond polarity & bond strength affects acidity. In binary compounds:  Bond Polarity (The higher the bond polarity, the stronger the bond, the weaker the acid) eg. ____  Bond Strength (The lower the bond strength, the higher the resulting H + ionization and the stronger the acid. ) eg. ____

Dissociation of Strong and Weak Acids

Acid Strength (continued)  A weak acid is not 100% ionized. For example acetic acid, CH 3 COOH,. Most acids, particularly organic acids, are weak acids.  A weak acid is not 100% ionized. For example acetic acid, CH 3 COOH, produces <100% H + (aq). Most acids, particularly organic acids, are weak acids.  Weak acids produce a much stronger conjugate base than water, eg. The acetate ion: (CH 3 COO  ) Weak Acids :

Multiprotic Acids  Monoprotic acids have 1 acidic H, diprotic have 2, eg. Sulfuric acid H 2 SO 4 etc.  In a strong multiprotic acid, like H 2 SO 4, only the first H is strong; transferring the second H is usually weak H 2 SO 4 + H 2 O  H 3 O +1 + HSO 4 -1 HSO H 2 O  H 3 O +1 + SO 4 -2

Aqueous Bases  Any compound that accepts a proton is a base.  The common bases are __________ metal hydroxide compounds. “Strong” and “weak” are used in the same sense for bases as for acids.  Strong = complete dissociation (100% hydroxide ion is supplied to the solution) An example of a weak base is ammonia. NH 3 (g) + H 2 O (l) NH 3 (aq) NH 4 + (aq) + OH - (aq) © Copyright R.J. Rusay

Bases (continued)  Weak bases have very little dissociation (or reaction with water), eg. methyl amine like ammonia has <100% hydroxide ion in aqueous solution.  H 3 CNH 2 (aq) + H 2 O(l)  H 3 CNH 3 + (aq) + ____(aq)  Organic bases are weak bases; for example, dopamine (neurotransmitter), cadaverine (product of cellular decomposition), morphine (narcotic pain killer) and cocaine are weak bases.

Natural Indicators

Reactions of Acids & Bases A use for natural indicators: “Neutralization Reactions” Titrations Constipation?

Neutralization Reactions How would indicator be used?

Aqueous Reactions: Neutralization Net Ionic Equations HCl (aq) + NaOH (aq) ---> NaCl (aq) + H 2 O (l) ___________________________________________________   HCl (aq) ---> H + (aq) + Cl - (aq)   NaOH (aq) ---> Na + (aq) + OH - (aq)   NaCl (aq) ---> Na + (aq) + Cl - (aq) ________________________________________________ Na + (aq) + OH - (aq) + H + (aq) + Cl - (aq) ---> Na + (aq) + Cl - (aq) + H 2 O (l) _______________________________________________________ © Copyright R.J. Rusay H + (aq) + OH - (aq) ---> H 2 O (l)

Stomach Chemistry

Acid-Base Titration Acids have pH 7, and 7 is neutralAcids have pH 7, and 7 is neutral Without a pH meter how can the progress of reaction be monitored?Without a pH meter how can the progress of reaction be monitored?

Acid-Base Titration pH & Water