ACIDS, BASES, AND pH

2 The solutions conduct electricity! They are called ELECTROLYTES HCl, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. Aqueous Solutions How do we know ions are present?

3 Aqueous Solutions weak electrolyte, like Acetic acid, ionizes only to a small extent, CH 3 CO 2 H(aq) CH 3 CO 2 H(aq)  CH 3 CO 2 - (aq) + H + (aq)  CH 3 CO 2 - (aq) + H + (aq)

4 Aqueous Solutions. Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugarethanol ethylene glycol Examples include: sugarethanol ethylene glycol

Acid Properties Sour taste (grape fruit) Sour taste (grape fruit) Found in many fruits Found in many fruits Vinegar Vinegar Will burn if not diluted Will burn if not diluted Made up of Nonmetals Made up of Nonmetals Acid formulas usually start with hydrogen- ex HCl, H 2 SO 4 Acid formulas usually start with hydrogen- ex HCl, H 2 SO 4

Base Properties Bitter taste Slippery feel Most household cleaners Also dangerous if not diluted Made up of a metal and nonmetals in formulas Arrhenius bases start with metals in their formulas and end with a OH- ex NaOH, KOH, Ba(OH) 2

Arrhenius Theory Substances ionize in water Substances ionize in water Acids, bases, and salts when dissolved in water, will conduct electricity. Acids, bases, and salts when dissolved in water, will conduct electricity. Called Electrolytes Called Electrolytes

Arrhenius Theory Acids release hydrogen ions (H + ) Acids release hydrogen ions (H + ) HCl → H + + Cl - HCl → H + + Cl - Bases release hydroxide ions (OH - ) Bases release hydroxide ions (OH - ) NaOH → Na + + OH -

9 Strong and Weak Acids/Bases Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO 3 (aq) + H 2 O(liq) ---> H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water.

10 HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. Strong and Weak Acids/Bases

Strong Acids will completely ionize

12 Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 CO 2 H Strong and Weak Acids/Bases

13 Strong Base: 100% dissociated in water. NaOH(aq) ---> Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO (lime) + H 2 O --> Ca(OH) 2 (slaked lime) CaO

15 Weak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O(liq) e NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

16 ACID-BASE THEORIES The most general theory for common aqueous acids and bases is the BRØNSTED - LOWRY theory ACIDS DONATE H + IONS BASES ACCEPT H + IONS

Bronsted Base: adds one hydrogen ion Bronsted Acid: removes one hydrogen ion Reactants Products

18 ACID-BASE THEORIES NH 3 is a BASE in water — and water is itself an ACID NH 3 / NH 4 + is a conjugate pair — related by the gain or loss of H + Every acid has a conjugate base - and vice-versa.

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20 Conjugate Pairs

You Practice NH 3 + H 2 O → NH OH - NH 3 + H 2 O → NH OH - HNO 3 + NaOH → H 2 O + NaNO 3 HNO 3 + NaOH → H 2 O + NaNO 3 NaHCO 3 + HCl → NaCl + H 2 CO 3 NaHCO 3 + HCl → NaCl + H 2 CO 3

Amphoteric A substance having the ability to act as an acid or a base A substance having the ability to act as an acid or a base or AmphoPROTIC Hydrogen ion = proton Water is an example Water is an example

Water is amphoprotic It can gain and lose a H+

Hydronium ion – An ion formed when a free H + forms with water to form an H 3 O + Hydronium ion – An ion formed when a free H + forms with water to form an H 3 O +

Why is Water Neutral? When one water gains, another loses a H+ [H 3 O+ ] = [OH-] [H 3 O+ ] = [OH-]

The pH scale only for water solutions Basic = more OH- Acidic = more H 3 O+ Neutral H 3 O+ = OH-

Relative ion concentrations pH is a relative measure of the hydrogen ion concentration pH is a relative measure of the hydrogen ion concentration pH is a rating; pH is a rating; ranges from 0 – 14 0 = most, 7 equal, 14 = least

Why at a pH = 7 ? Determined by concentration [ X ] of each ion Determined by concentration [ X ] of each ion [H+ ]= [OH-] = M The concentration of hydrogen ion equals the concentration of hydroxide ion equals ten to the negative seventh molar concentration Need to remember molarity and concentration

31 [H 3 O + ], [OH - ] and pH A common way to express acidity and basicity is with pH pH = - log [H 3 O + ] In a neutral solution, [H 3 O + ] = [OH - ] = 1.00 x at 25 o C pH = -log (1.00 x ) = - (-7) = 7

Relative ion concentrations pOH is a relative measure of the hydroxide ion concentration pOH is a relative measure of the hydroxide ion concentration pOH is a rating; pOH is a rating; ranges from 0 – 14 0 = most, 7 equal, 14 = least

Any pX Scales In general pX = -log X pOH = - log [OH - ] pH = - log [H + ] pH = - log [H + ]

Determining pOH pH + pOH = 14 If know one can determine the other. If pH = 13, what is the pOH? 13 + pOH = 14 pOH = 14 – 13 = 1