1 Acids and Bases

Topics to be covered Acids and Bases Arrhenius definition Bronsted-Lowry definition pH Strong vs weak acids Neutralization reactions

Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

Acid Nomenclature Review No Oxygen  w/Oxygen An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

Acids and Bases: Theory Arrhenius theory of acids Arrhenius definition of an acid: any compound that contains hydrogen and produces H + (H 3 O + when reacts with water) ions when dissolved in water. A strong acid is a water-soluble compound that completely dissociates to give H 3 O + ions. A weak acid is a water-soluble compound that dissociates only partially, producing few H 3 O + ions.

Acids and Bases: Theory Arrhenius theory of acids A strong acid is a water-soluble compound that completely dissociates to give H 3 O + ions. A weak acid is a water-soluble compound that dissociates only partially, producing few H 3 O + ions.

Rafa Muñoa Lizardi Institutua Zarautz Acids and Bases: Theory Arrhenius theory of bases Arrhenius definition of a base: any compound that contains a metal and hydroxide (OH - ) group produces OH - (hydroxide) ions when dissolved in water. All hydroxides are strong bases because their dissociation reaction go essentially to completion.

Acids and Bases: Theory Bronsted-Lowry theory of acids and bases They proposed that acids and bases can be defined in terms of their ability to transfer protons. An acid is a substance (molecule or ion) that can transfer protons to another substance. A base is a substance than can accept a proton.

Acids and Bases: Theory Bronsted-Lowry theory of acids and bases An acid and a base always work together to transfer a proton. In other words, a substance can function as an acid only if another substance simultaneously behaves as a base.

Acids and Bases: Theory Bronsted-Lowry theory of acids and bases Some substances can act as an acid in one reaction and as a base in another. For example, H 2 O is a Bronsted-Lowry base in its reaction with HCl and a Bronsted-Lowry acid in its reaction with NH 3. Those substances are called amphoteric.

Acids and Bases: Theory Bronsted-Lowry theory of acids and bases To be a Bronsted-Lowry acid, a molecule or ion must have a hydrogen atom that it can lose as H + ion. To be a Bronsted-Lowry base, a molecule or ion must have a nonbonding pair of electrons that it can use to bind the H + ion.

ACID-BASE THEORIES The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID

Conjugate Pairs

Some Common Acids HCl hydrochloric acid HNO 3 nitric acid H 3 PO 4 phosphor ic acid H 2 SO 4 sulfur ic acid CH 3 COOH acet ic acid

Learning Check AB3 Give the names of the following A. HBr (aq)1. bromic acid 2. bromous acid 3. hydrobromic acid B. H 2 CO 3 1. carbonic acid 2. hydrocarbonic acid 3. carbonous acid

Solution AB3 A. HBr3. hydrobromic acid The name of a nonoxy acid begins with the prefix hydro- and ends with -ic acid. In a nonoxy acid, the negative anion end in -ide. B. H 2 CO 3 1. carbonic acid The name of an oxyacid is named with the stem of the anion (carbonate) changed to -ic acid

Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH -  Cl - + H 2 O H 2 O + H 2 SO 4  HSO H 3 O + AcidAcid AcidAcid BaseBase BaseBase Conj. Base Conj. Acid

Some Common Bases NaOHsodium hydroxide KOH potassium hydroxide Ba(OH) 2 ________________________ Mg(OH) 2 ________________________ Al(OH) 3 aluminum hydroxide

LecturePLUS Timberlake Learning Check AB4 Match the formulas with the names: A. ___ HNO 2 1) hydrochloric acid B. ___Ca(OH) 2 2) sulfuric acid C. ___H 2 SO 4 3) sodium hydroxide D. ___HCl4) nitrous acid E. ___NaOH5) calcium hydroxide

Solution AB4 Match the formulas with the names: A. _4__ HNO 2 1) hydrochloric acid B. _5__Ca(OH) 2 2) sulfuric acid C. _2__H 2 SO 4 3) sodium hydroxide D. _1__HCl4) nitrous acid E. _3__NaOH5) calcium hydroxide

Learning Check AB5 Acid, Base Name or Salt CaCl 2 _______________________ KOH_______________________ Ba(OH) 2 ______ _________________ HBr_______________________ H 2 SO 4 ________________________

Solution AB5 Acid, Base Name or Salt CaCl 2 saltcalcium chloride KOHbasepotassiuim hydroxide Ba(OH) 2 basebarium hydroxide HBracidhydrobromic acid H 2 SO 4 acidsulfuric acid

pH Scale

pH The Power of Hydrogen Measures the acidity or basicity of a solution pH = -log[H + ] [H + ] = 10 -pH pOH = -log[OH - ] [OH - ] = 10 -pOH

Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X pH = - log 1 X pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

Try These! Find the pH of these: 1)A 0.15 M solution of Hydrochloric acid 2) A 3.00 X M solution of Nitric acid pH = - log [H+] pH = - log 0.15 pH = - (- 0.82) pH = 0.82 pH = - log 3 X 10-7 pH = - (- 6.52) pH = 6.52

pH calculations – Solving for H+ If the pH of Coke is 3.12, [H + ] = ??? Because pH = - log [H + ] then - pH = log [H + ] - pH = log [H + ] Take antilog (10 x ) of both sides and get 10 -pH = [H + ] [H + ] = = 7.6 x M *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

pOH Since acids and bases are opposites, pH and pOH are opposites!Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH.pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a basepOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

What is the pH of a 2 x M HNO 3 solution? HNO 3 is a strong acid – 100% dissociation. HNO 3 (aq) + H 2 O (l) H 3 O + (aq) + NO 3 - (aq) pH = -log [H + ] = -log [H 3 O + ] = -log(0.002) = 2.7 Start End M 0.0 M What is the pH of a 1.8 x M Ba(OH) 2 solution? Ba(OH) 2 is a strong base – 100% dissociation. Ba(OH) 2 (s) Ba 2+ (aq) + 2OH - (aq) Start End M M0.0 M pH = – pOH = – 1.44 = 12.56

Acid-Base Indicators Weak acids that undergo a colour change as the pH changes

Percentage Ionization Not all acids (or bases) undergo complete ionization or dissociation. Acids and bases that partially ionize are called "weak" acids or bases e.g. Acetic Acid, HC 2 H 3 O 2 is a weak acid Ammonia, NH 3, is a weak base

Read pgs Do # 6, 7, 10, 15, 16 on page 463

References Rafa Muñoa W Sautter McGraw Hill Ryerson 11 Nelson, Chemistry 11