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
Bronsted-Lowry acid: acid is a proton (H + ) (hydrogen ion) donor. HA(aq) A - (aq) + H + (aq) H Cl H + O O H H H H Cl
Properties of Acids ABOVE CAN REPLACE BELOW 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 + 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.
acid rain (NO x, SO x ) ph of 4.2-4.4 in Washington DC area ph 0-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12 acidic (H + ) > (OH - ) normal rain (CO 2 ) ph = 5.3 5.7 neutral @ 25 o C (H + ) = (OH - ) distilled water fish populations drop off ph < 6 and to zero ph < 5 basic or alkaline (H + ) < (OH - ) natural waters ph = 6.5-8.5
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 acids release few hydrogen ions in water Strong acids: HOCl + H 2 O H 3 O + + ClO - hydrochloric sulfuric nitric HCl H 2 SO 4 HNO 3 hydrobromic hydroiodic Perchloric chloric HBr HI HClO 4 HClO 3
Complete dissociation of Acids HA What happens to the HA molecules in solution?
100% dissociation of Acid HA H + Strong Acid A - Would the solution be conductive?
Partial dissociation of HA HA H + A - Weak Acid Would the solution be conductive?
HA H + + A - HA H + A - Weak Acid 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? Dissolved carbon dioxide lowers the ph CO 2 (g) + H 2 O H 2 CO 3 H + + HCO 3 - 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 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 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 4+ + OH -
Bronsted-Lowry Bases: base is a substance that can accept a proton (H + ) NaOH(aq) Na + (aq)+oh - (aq) H H + H N H H H O H N H H O H
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 Strong Bases: NH 3 + H 2 O NH 4+ + OH - RbOH Rubidium hydroxide LiOH NaOH KOH Lithium hydroxide Sodium hydroxide Potassium hydroxide Ca(OH) 2 Ba(OH) 2 Sr(OH) 2 Calcium hydroxide Barium hydroxide Strontium hydroxide If it is not a strong base then it is a weak base!! CsOH Cesium 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 Ca(OH) 2 NH 4 OH lithium hydroxide calcium hydroxide ammonium hydroxide
Conjugates & Amphoteric substances
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 + H 2 O Cl + H 3 O + acid base conjugate base conjugate acid
Amphoteric Substance Amphoteric substance: Substance that can either donate or accept a hydrogen ion. Conjugate Base OH hydroxide H + + H + H 2 O Conjugate Acid H 3 O + hydronium H + SO 2 H+ + H + 4 HSO H 2 SO 4 4-2 -1 0 +1 +2 CO 2 3 H+ + H + HCO 3 H 2 CO 3
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).
Hydronium ion [H 3 O + ] and hydroxide ion [OH - ]
Acidity and Bascitiy The concentration of hydronium H 3 O + solution expresses its acidity. The concentration of hydroxide solution expresses its basicity. OH ions in a ions in a When the concentration of H 3 O + goes up, the concentration of OH goes down, and vice versa.