Acids

Definition of Acid HCl + H2O  H3O+ + Cl– Acids are substances that contain H+ ions that ionize when dissolved in water. Arrhenius acid: a compound that increases the concentration of H+ ions that are present when added to water. These H+ ions form the hydronium ion (H3O+) when they combine with water molecules HCl + H2O  H3O+ + Cl–

– + Bronsted-Lowry acid: acid is a proton (H +) (hydrogen ion) donor. HA(aq)⇌A-(aq) + H +(aq) H Cl O – +

ABOVE CAN REPLACE BELOW Properties of Acids ABOVE CAN REPLACE BELOW Acids eat away (oxidize) active metals Metals like Li, Mg and Zn can be oxidized by an acid to produce hydrogen gas. The three metals listed below hydrogen (Cu, Ag and Au) cannot be oxidized by an acid. This is a single replacement reaction: 2 Li + 2 HCl  2 LiCl + H2 Ca + 2HCl  CaCl2 + H2 The active metal kicks out the hydrogen in the acid.

b) Acids have a pH less than 7. pH is a scale that measures the acidity or alkalinity of a solution. A pH of 7 is a neutral solution, and acids have a pH of less than 7 Each decrease of one in pH is a tenfold increase in acid strength. An acid with a pH of 3 is ten times more acidic than one with a pH of 4, and one hundred times more acidic than a solution with a pH of 5.

pH acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area 0-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12 acidic (H+) > (OH-) neutral @ 25oC (H+) = (OH-) distilled water basic or alkaline (H+) < (OH-) normal rain (CO2) pH = 5.3 – 5.7 fish populations drop off pH < 6 and to zero pH < 5 natural waters pH = 6.5 - 8.5

Strong acids: c) Acidic solutions conduct electricity. Acids are electrolytes, because they form ions in solution. Strong acids ionizes completely in water, conducts electricity well HCl  H+ + Cl- Weak acids release few hydrogen ions in water HOCl + H2O ↔ H3O+ + ClO- Strong acids: HCl H2SO4 HNO3 HBr HI HClO4 hydrochloric sulfuric nitric chloric HClO3 hydrobromic hydroiodic Perchloric

Complete dissociation of Acids CHM 101 Sinex Complete dissociation of Acids HA What happens to the HA molecules in solution?

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

d) Dilute solutions of acids taste sour. e) Acids react with carbonates to form CO2, salt and water vapor Baking soda and vinegar: NaHCO3 (s) + HC2H3O2 (aq)  CO2 (g) + H2O (l) + NaC2H3O2 (aq) This is the “volcano” reaction, the CO2 gas given off causes the solution to foam up and out.

f) Acids can be formed by reaction of gaseous oxides with water Burning fossil fuels releases nonmetallic oxides (CO2, NO2, SO2 and similar molecules) into the atmosphere. When they combine with the water in the atmosphere, they form weak acids that can cause ecological problems. Plants and fish thrive in a narrow range of pH values.

What is acid rain? Dissolved carbon dioxide lowers the pH CO2 (g) + H2O  H2CO3  H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O …  HNO3 both strong acids SO2, SO3 + H2O …  H2SO4 pH < 5.3

HCl Naming Acids Hydrochloric acid Binary Acids: hydro- prefix, followed by nonmetal ion name with last syllable replaced with –ic acid HCl hydro +chloride – ide + ic acid Hydrochloric acid

HNO3 HNO2 Naming Acids Nitric acid Nitrous acid + ic acid + ous acid Ternary Acids: no hydro- prefix, polyatomic ion name followed by –ic acid, if ion ends in -ide, –ate Polyatomic ion name followed by –ous acid if ion ends in –ite HNO3 HNO2 nitrate + ic acid nitrite + ous acid Nitric acid Nitrous acid

Bases

Bases Bases are substances that contain hydroxide (OH-1) ions dissolved in aqueous solution. Arrehnius Base: a compound that increases the concentration of (OH-) hydroxide ions when added to water NH3 + H2O  NH4+ + OH-

Bronsted-Lowry Bases: base is a substance that can accept a proton (H+) NaOH(aq)→Na+ (aq)+OH- (aq) H N O – +

Properties of Bases a) Bases have a pH greater than 7 pH is a scale that measures the acidity or alkalinity (basicity) of a solution. A pH of 7 is a neutral solution, and bases have a pH of more than 7. Each increase of one in pH is a tenfold increase in base strength. A base with a pH of 10 is ten times more basic than one with a pH of 9, and one hundred times more basic than a solution with a pH of 8.

If it is not a strong base then it is a weak base!! b) Basic solutions conduct electricity. Bases are electrolytes, because they form ions in solution. Strong bases ionizes completely in water NaOH  Na+ + OH- Weak bases releases few hydroxide in water NH3 + H2O ↔ NH4+ + OH- Strong Bases: LiOH NaOH KOH Ca(OH)2 Ba(OH)2 Sr(OH)2 If it is not a strong base then it is a weak base!! RbOH Rubidium hydroxide CsOH Cesium hydroxide Lithium hydroxide Sodium hydroxide Potassium hydroxide Calcium hydroxide Barium hydroxide Strontium hydroxide

c) Bases taste bitter d) Bases can be formed when Group 1 and 2 metals react with water, hydrogen is released too. 2 Na (s) + H2O (l) ↔ 2 NaOH (aq) + H2 (g) Mg (s) + 2 H2O (l) ↔ Mg(OH)2 (aq) + H2 (g) e) Bases hydrolyze fats (turns them into soap, also called “saponification”) Ammonium hydroxide (NH3 (aq) or NH4OH) is a solution used to clean floors and countertops of greasy buildup or residue.

LiOH lithium hydroxide Ca(OH)2 calcium hydroxide Naming bases Name the metal CATION first; it keeps its name as listed in the Periodic Table. The polyatomic ion "hydroxide" (OH-) also keeps its name. Examples: LiOH lithium hydroxide Ca(OH)2 calcium hydroxide NH4OH ammonium hydroxide

Conjugates & Amphoteric substances

Acid- conjugate base base- conjugate acid Acid, Base Conjugates Acids are proton (H+) donors. Bases are proton (H+) acceptors. Conjugate acid – base pair: The pair of acid and base that differ by a H+. Acid- conjugate base base- conjugate acid HCl + H2O  Cl– + H3O+ acid conjugate base base conjugate acid

H+ Amphoteric Substance H2O H3O+ OH– SO42– ↔ ↔ H2SO4 HSO4– CO32– ↔ ↔ Amphoteric substance: Substance that can either donate or accept a hydrogen ion. Conjugate Base Conjugate Acid – H+ + H+ H+ OH– hydroxide H2O H3O+ hydronium ↔ ↔ SO42– ↔ – H+ + H+ ↔ H2SO4 HSO4– -2 -1 +1 +2 CO32– ↔ – H+ + H+ ↔ H2CO3 HCO3–

Determination of Acids and Bases

How to determine acids and bases pH probes pH probes contain an electrode that detects electrical conductivity. Before using this electronic device, it has to be calibrated by giving it a taste of two different solutions with different pH’s. These come in pocket devices that run on batteries or in computer interface probe form.

2. Acid-Base Indicators and narrowing down pH using multiple indicators Methyl orange is RED from a pH of 3.2 or lower, and YELLOW from a pH of 4.4 or more. The middle of the range is an intermediate color (in this case, ORANGE).

Hydronium ion [H3O+] and hydroxide ion [OH-]

Acidity and Bascitiy The concentration of hydronium ions in a solution expresses its acidity. The concentration of hydroxide ions in a solution expresses its basicity. H3O+ OH– When the concentration of H3O+ goes up, the concentration of OH− goes down, and vice versa.

Water dissociation constant H2O(l) + H2O (l) ↔ H3O+ (aq) + OH– (aq) Keq = [H3O+][OH–] Equilibrium constant Kw = [H3O+][OH–] Water dissociation constant [H3O+] = [OH−] = 1.00 × 10−7 M Kw = [H3O+][OH–] = 1 x 10 -14 In impure water (contains an acidic or basic substance): If [H3O+] > 1.0 x 10-7 M, solution is acidic. If [H3O+] < 1.0 x 10-7 M, solution is basic If [H3O+] = 1.0 x 10-7 M, solution is neutral.

Click Below for the Video Lectures Acid and Base Equilibrium

pH, pOH

- log 10x 10x pH, pOH, kw, [H3O+],[OH-] 14 1 x 10 14 pH pOH [H3O+]

* * A. The [H3O+] of tomato juice is 1 x 10-4 M. What is the pH of the solution? - 4 b) 4 c) 8 pH = -log[H3O+] = -log [1x10-4] = 4 B. The [OH-] of an ammonia solution is 1 x 10-3 M. What is the pH of the solution? a) 3 b) 11 c) -11 pOH = -log[OH-] = -log [1x10-3] = 3 pH + pOH = 14 pOH = 14-pH = 14-3 = 11 * *

Acid and Base Neutralization

HCl (aq) + NaOH (aq) ↔ NaCl (aq) + HOH (l) Neutralization When acidic and basic solutions are mixed, the H+ of the acid and the OH- of the base combine to form water. The anion of the acid and the cation of the base come together to form a salt. HCl (aq) + NaOH (aq) ↔ NaCl (aq) + HOH (l) Acid Base Salt Water

Click Below for the Video Lectures Neutralization Reaction