Chapter 15: Acids & Bases

Properties of Acids & Bases Acids 1.Aqueous solns of acids have a SOUR taste. 2.Has many indicators but most common is LITMUS PAPER… turns Blue to Red 3.Some acids react with metals to release H 2 gas 4.Acids react with Bases to produce salts & H 2 O (neutralized soln) 5.Some acids conduct electric currents Bases 1.Aqueous soln tastes bitter 2.Bases have many indicators but most common is LITMUS PAPER… turns Red to Blue 3.Bases do not react with metals 4.React with acids to produce salts & H 2 O 5.Bases conduct electric current 6.Dilute aq soln of bases feel slippery

Acid Nomenclature Review Most acids fall into one of 3 categories: – Binary Acids: a H and an element from Group 6A or 7A ( a the oxygen group or a halogen) – Oxy Acids: contains H, O and some other element – Carboxylic Acids: organic acids (they contain Carbon).

Naming acids (a review) Binary acids- acids that are made of only two elements (no Oxygen) – A. Prefix is always hydro – B. Name the second element with the suffix- ic EX: HClHydrochloric acid H 2 S

Ternary acids- those acids that are made of more than two elements; usually contain a polyatomic ion (have Oxygen) These can be oxy acids and carboxylic acids – A. For the acid containing the most common polyatomic ion of its group simply use the first part of the polyatomic name and follow with the suffix ic. – B. polyatomic with one less oxygen than the ic, use the suffix ous. – C. polyatomic with two less oxygen than the ic, use the prefix hypo and the suffix ous. – D. polyatomic with one more oxygen than the ic, use the prefix per and the suffix ic.

Examples of Acid Naming Rules Rule 1: acids with `ic' suffix represent natural `ate' polyatomic ions HBrO 3 bromic acid HClO 3 chloric acid Rule 2: when an extra oxygen is added, add a `per' prefix to name HBrO 4 perbromic acid HClO 4 perchloric acid Rule 3: when 1 oxygen is taken away (from `ate' ion to ‘ite’ ion), change the `ic' suffix to `ous' HBrO 2 bromous acid HClO 2 chlorous acid Rule 4: when 2 oxygens are taken away, change the `ic' suffix to `ous' and add a `hypo' prefix HBrO hypobromous acid HClO hypochlorous acid

Common Industrial Acids Sulfuric Acid : Most commonly produced acid (47 million tons / year). Used is oil refineries, metallurgy and to manufacture fertilizers, metals, paper, paint, dyes, detergents, sugar, etc. IT is the acid in car batteries. Nitric Acid: Volatile & unstable, it stains proteins yellow, has a suffocating odor and causes serious burns. Used to make explosives, rubber, plastics, dyes and pharmaceuticals.

Phosphoric Acid: Used to manufacture fertilizers, animal feed, detergents & ceramics. Diluted it’s sour and used in sodas and for cleaning. Hydrochloric Acid: Produced in the stomach for digestion, it is also used for cleaning, food production, activation of oil wells. Dilute- called muriatic acid. Acetic Acid: Concentrated- called glacial acetic acid.

Arrhenius Acids & Bases Swedish Chemist, Svante Arrhenius, defined acids and bases in water Acid- substance that dissociates in water to produce hydrogen ions (H + ) water Base- substance that dissociates in water to produce hydroxide ions (OH - )

Common Arrhenius Acids & Bases AcidFormulaBaseFormula Hydrochloric acidHClSodium hydroxideNaOH Nitric acidHNO 3 Potassium hydroxide KOH Acetic acidHC 2 H 3 O 2 Magnesium hydroxide Mg(OH) 2 Sulfuric acidH 2 SO 4 Calcium hydroxideCa(OH) 2 Carbonic acidH 2 CO 3 Barium hydroxideBa(OH) 2 Phosphoric acidH 3 PO 4

The Hydronium Ion Because H + will combine with water… a Hydronium ion is actually created. Water acts as an acid and a base… substances that do so are called amphoteric.

Strong & Weak Acids Strong acids disassociate 100%. Ex. HCl – HCl + H 2 O → H 3 O + + Cl - 100% – Excellent conductors Weak Acids only disassociate a small amount. Ex. HC 2 H 3 O 2 – HC 2 H 3 O 2 + H 2 O ↔ H 3 O + + C 2 H 3 O % – Poor conductors

Strong & Weak Bases Strong bases: Disassociates 100%. This is called an alkaline soln. They have the strongest affinity for H + meaning they react 100% with water. Ex. CaO – O 2- + H 2 O → 2OH - Weak bases: only partially disassociate /react with water. Ex. CO 3 2- – CO H 2 O ↔ HCO OH -

15.2 Acid-Base Theories The Arrhenius definition of acids and bases are good, but it doesn’t describe all chemicals that are acids and bases. Remember Arrhenius said that they have to be in solution with H 2 O. Some chemicals will act as an acid or a base in solution with something other than H 2 O.

The Brønsted-Lowry Definition In 1923, two chemists independently developed a new definition of acids and bases. Danish Chemist, Johannes Brønsted and English Chemist, Thomas Martin Lowry said: An acid is any substance that can donate H + ions A base is any substance that can accept H + ions

Brønsted-Lowry expands the definition of Arrhenius acids/bases. 1.Defines acids/bases independently of how they behave in water. 2.Focuses only on the H + ions and ignores the OH - ions.

Monoprotic acid- an acid that only donates ONE proton (H + ) per molecule. Ex: HCl Polyprotic acids- an acid that can donate MORE than one proton per molecule. Ex: H 3 PO 4

Lewis Acids & Bases In 1923, G.N. Lewis defined an acid and a base by the donation of electron pairs. Lewis acid- an atom, ion or molecule that ACCEPTS an ELECTRON PAIR to form a covalent bond. Lewis base- an atom, ion or molecule that DONATES an ELECTRON PAIR to form a covalent bond. Lewis acid-base reaction- the formation of 1 or more bonds between and electron-pair donor & an electron-pair acceptor.

15.3 Conjugate Acid-Base Pairs Conjugate means… joined together or coupled. An acid and a base which differ by a proton are said to form a conjugate acid base pair or the pairs of substances which can be formed from one another by the gain or loss of protons are known as conjugate acid base pairs.

Strength of Conjugate Acid-Base Pairs The stronger the acid the weaker the conjugate base and vice versa.

Acid-Base Properties of Salts When salts disassociate in water, they break down into cations and anions. – NaCl + H 2 O → Na + + Cl - Many of these ions are weak Brønsted-Lowry acids or bases. Salt hydrolysis reactions- rxn of ions from salts to form H or OH -

We can predict if the salt soln. will be acidic (formed H ) or basic (formed OH - ) Salts of: – STRONG acids + STRONG bases = neutral soln. – STRONG acids + weak bases = acidic soln. formed H – Weak acids + STRONG bases = basic soln. formed OH - – Weak acids + weak bases = neutral soln.

16.1 The Self-ionization of Water and pH Pure water does not have H 2 O molecules only. It also contains H 3 O + ions and OH - ions. Water is amphoteric, can act as an acid or a base with other chemicals. Self-ionization-

Mathematical Definition “In pure water at 25°C, both H 3 O + and OH - ions are found at concentrations of 1.0 X M.” K w = [H 3 O + ] [OH - ] K w = 1.0 X – [H 3 O + ] = 1.0 X – [OH - ] = 1.0 X X [H 3 O + ] > 1.0 X > [OH - ] Acidic Soln 1.0 X both = 1.0 X Neutral soln 1.0 X [OH - ] > 1.0 X > [H 3 O + ] Basic Soln

Practice Problems If the concentration of H 3 O + in blood is 4.0x10 -8 M, the blood is acidic, basic or neutral? – What is the concentration of OH - ions? What is the concentration of OH - ions in chocolate milk if [H 3 O + ] = 4.5x10 -7 M? – Is it acidic, basic, or neutral? What is the concentration of H 3 O + ions in black coffee if [OH - ] = 1.3x10 -9 M. – Is it acidic, basic, or neutral?

The pH Scale In 1909, Søren Sørensen developed the pH scale. – 0-6.9: acid – : base Its based on logarithms: pH= -log [H 3 O + ] Using a calculator, try: -log(8.7 x ) What is the pH of a soln with [H 3 O + ] = 7.3x10 -5 M? [H 3 O + ] = 6.23x10 -4 M? [OH-] = 5.0x10 -2 M? (14=pH + pOH)

Measuring pH 2 Common methods 1.Use an indicator, (litmus paper) – can use a combination of indicators to get a more precise pH reading 2.Use an pH meter.

Some Acid-Base Indicators