Acids

Definition of Acid 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 (H 3 O + ) when they combine with water molecules HCl + H 2 O  H 3 O + + Cl –

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

Properties of Acids a)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 + H 2 Ca + 2HCl  CaCl 2 + H 2 – The active metal kicks out the hydrogen in the acid. ABOVE CAN REPLACE BELOW

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 o C (H + ) = (OH - ) distilled water acidic (H + ) > (OH - ) basic or alkaline (H + ) < (OH - ) natural waters pH = normal rain (CO 2 ) pH = 5.3 – 5.7 acid rain (NO x, SO x ) pH of in Washington DC area 0-14 scale for the chemists fish populations drop off pH < 6 and to zero pH < 5

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 bases releases few hydroxide in water HOCl + H 2 O ↔ H 3 O + + ClO - Strong acids: HClH 2 SO 4 HNO 3 HBrHIHClO 4 If it is not a strong base then it is a weak base!! hydrochloricsulfuric nitric hydrobromichydroiodic perchloric

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

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

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

HA H+H+ A-A- Weak Acid HA  H + + 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 CO 2, salt and water vapor – Baking soda and vinegar: NaHCO 3 (s) + HC 2 H 3 O 2 (aq)  CO 2 (g) + H 2 O (l) + NaC 2 H 3 O 2 (aq) – This is the “volcano” reaction, the CO 2 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 (CO 2, NO 2, SO 2 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? CO 2 (g) + H 2 O  H 2 CO 3  H + + HCO 3 - Dissolved carbon dioxide lowers the pH Atmospheric pollutants from combustion NO, NO 2 + H 2 O …  HNO 3 SO 2, SO 3 + H 2 O …  H 2 SO 4 both strong acids pH < 5.3

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

Naming Acids Tertiary 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 HNO 3 nitrate + ic acid Nitric acid HNO 2 nitrite + ous acid Nitrous acid

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 NH 3 + H 2 O  NH OH -

H H H H H H N NO O – + H H H H Bronsted-Lowry Bases: base is a substance that can accept a proton (H + ) NaOH(aq)→Na + ( aq)+OH - (aq)

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.

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 NH 3 + H 2 O ↔ NH OH - Strong Bases: LiOH NaOHKOH Ca(OH) 2 Ba(OH) 2 Sr(OH) 2 If it is not a strong base then it is a weak base!! Lithium hydroxideSodium hydroxidePotassium hydroxide Calcium hydroxideBarium hydroxideStrontium 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) + H 2 O (l) ↔ 2 NaOH (aq) + H 2 (g) – Mg (s) + 2 H 2 O (l) ↔ Mg(OH) 2 (aq) + H 2 (g) e) Bases hydrolyze fats (turns them into soap, also called “saponification”) – Ammonium hydroxide (NH 3 (aq) or NH 4 OH) is a solution used to clean floors and countertops of greasy buildup or residue.

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 NH 4 OH ammonium hydroxide

Conjugates & Amphoteric substances

Acid, Base Conjugates HCl + H 2 O  Cl – + H 3 O + 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 conjugate acid conjugate base baseacid

Amphoteric Substance Amphoteric substance: Substance that can either donate or accept a hydrogen ion. H2OH2O ↔ – H + + H + ↔ OH – hydroxide H3O+H3O+ hydronium SO 4 2– ↔ – H + + H + ↔ H 2 SO 4 HSO 4 – CO 3 2– ↔ – H + + H + ↔ H 2 CO 3 HCO 3 – Conjugate BaseConjugate Acid H+H+

Determination of Acids and Bases

How to determine acids and bases 1.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).

[H 3 O + ] [OH - ] and K w

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. When the concentration of H 3 O + goes up, the concentration of OH − goes down, and vice versa.

Water dissociation constant H 2 O (l) + H 2 O (l) + OH – (aq) ↔H 3 O + (aq) K eq = [H 3 O + ][OH – ] Equilibrium constant Water dissociation constant K w = [H 3 O + ][OH – ] [H 3 O + ] = [OH − ] = 1.00 × 10 −7 M K w = [H 3 O + ][OH – ] = 1 x In impure water (contains an acidic or basic substance): If [H 3 O+] > 1.0 x M, solution is acidic. If [H 3 O+] < 1.0 x M, solution is basic If [H 3 O+] = 1.0 x M, solution is neutral.

Click Below for the Video Lectures Acid and Base Equilibrium

pH, pOH

pH, pOH, k w, [H 3 O + ],[OH - ] [H 3 O + ][OH - ] pHpOH - log 1 x x 14

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

Acid and Base Neutralization

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