Acids and Bases

General properties ACIDS Taste sour Turn litmus React with active metals – Fe, Zn React with bases BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids blue to red red to blue

More properties ACIDS Feel and look like water Conduct electricity (electrolytes) when dissolved in water Burn or sting Usually formula starts w/ H BASES do not react with metals Can be strong or weak electrolytes in water Do not sting or burn

Definitions Acids – produce H+ Arrehenius Bases - produce OH- Acids – donate H+ Bases – accept H+ Arrehenius only in water Bronsted-Lowry any solvent

Why is H+ a proton? *H is made of 1 proton and 1 electron *When H loses an e-, all that is left is a proton.

Examples The hydrogen ion in aqueous solution H+ + H2O  H3O+ (hydronium ion) Examples Arrhenius HCl NaOH Bronsted-Lowry HCl HCN NH3

Conjugate acid/base pairs Conjugate acid –acid that forms after the original base accepts an H+ Conjugate base –base that forms after the original acid donates an H+ NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)

Conjugate acid/base pairs **Notice how water is an ACID in the first reaction and BASE in the other reaction *water is called AMPHOTERIC

Show how water can be amphoteric. Water is a mixture of H2O, H+ and OH-

The Bronsted-Lowry Concept Conjugate pairs HCl Cl- CH3COOH CH3COO- NH4+ NH3 HNO3 NO3- How does a conjugate pair differ? H+ transfer

Neutralization HCl + NaOH  NaCl + HOH HCl + Mg(OH)2  In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH HCl + Mg(OH)2  H2SO4 + NaHCO3 

Let’s examine the behavior of an acid, HA, in aqueous solution. CHM 101 Let’s examine the behavior of an acid, HA, in aqueous solution. Sinex HA What happens to the HA molecules in solution?

100% dissociation of HA HA H+ Strong Acid A- Would the solution be conductive?

Partial dissociation of HA Weak Acid A- Would the solution be conductive?

At any one time, only a fraction of the molecules are dissociated. HA  H+ + A- HA H+ Weak Acid A- At any one time, only a fraction of the molecules are dissociated.

Strong and Weak Acids/Bases Strong acids/bases – completely dissociates into ions HCl NaOH HNO3 KOH H2SO4 Weak acids/bases – only partial dissociation, both ions and molecules CH3COOH NH3

Calculations ↕ OH- ↔ pOH 4 different values to find: pH (this indicates if it’s ACID/BASE/NEUTRAL) pOH H+ (hydrogen ions) or H3O+ (hydronium ions) OH- (hydroxide ions) H+ ↔ pH ↕ OH- ↔ pOH

Calculations What is pH? The power of hydrogen (used to determine if solution is and acid, base or neutral) What is pOH? The power of hydroxide What is [H+]? The molarity of acid ions in a solution What is [OH-]? The molarity of base ions in a solution

pH = -log[H3O+]* pOH = -log[OH-] pH + pOH = 14 *or [H+] pOH = -log[OH-] pH + pOH = 14

[H+]= 10^(-pH) [OH-] = 10^(-pOH) How to check your work: [H3O+][OH-] = 1.0  10-14 pH + pOH = 14

pH of Common Substances

What is the pH of 0.050 M HNO3? pH = -log[H3O+] pH = -log[0.050] Acidic or basic? Acidic

Example Find the pH, pOH, & [OH- ] if [H+]= 3.25x10-4 M

What is the molarity (concentration) of HBr in a solution that has a pOH of 9.6? pH + pOH = 14 pH + 9.6 = 14 pH = 4.4 pH = -log[H3O+] 4.4 = -log[H3O+] -4.4 = log[H3O+] [H3O+] = 4.0  10-5 M HBr Acidic

pH pOH [H+] [OH―] Acid/Base /Neutral   3.21 5.87 2.51 x 10-2 M .00875 M

Testing pH in the Lab Litmus paper Indicators pH meter

Indicators dyes that will change color in the presence of an acid or base. Color changes occur when the molecules are ionized (acting as an acid) or un-ionized (acting as a base). Indicators change color during specific pH ranges

Some of the many pH Indicators and their pH range

Titration A laboratory method for determining the concentration of an unknown acid or base using a neutralization reaction. A standard solution,(a solution of known concentration), is used.

Titration Terminology Equivalence point - The point at which there are equal concentrations of acid and base. [H+] = [OH-] End point – the point at which the chosen indicator changes color to mark a change in pH (also called indication point)

Equivalence Point

Solving Titration Problems Use the titration formula MaVa = MbVb What is the concentration of HCl if 30.0 mL of 0.10 M NaOH neutralizes 50.0mL HCl?