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ACIDS, BASES, &
SALTS
What is an ACID?• pH less than 7• Neutralizes bases• Forms H + ions in solution• Corrosive-reacts with most metals to form hydrogen gas
• Good conductors of electricity
Acids Generate Ions
HNO3 + H2O H3O+ + NO3
Common Acids • HCl- hydrochloric- stomach acid• H2SO4- sulfuric acid - car
batteries• HNO
3 – nitric acid - explosives
• HC2H3O2- acetic acid - vinegar
• H2CO3-carbonic acid – sodas
• H3PO4- phosphoric acid -flavorings
Strong Acids
Strong Acids are Strong Electrolytes They dissociate completely in water. 100% of the HA molecules break up into H+ and A- ions.
There are six common strong acids chemists MUST know:
1. HCl - Hydrochloric Acid2. HI - Hydroiodic Acid3. HBr - Hydrobromic Acid4. HNO3 - Nitric Acid
5. HClO3 - Chloric Acid
6. H2SO4 - Sulfuric Acid *1st dissociation only
Weak Acids
Weak Acids are Weak Electrolytes They DO NOT dissociate completely in water. 1% of the HA molecules break up into H+ and A- ions.
There are five common weak acids chemists MUST know:
1. HF - Hydrofluoric Acid2. H3PO4 - Phosphoric Acid *1st dissociation only
3. HC2H3O2 - Acetic Acid
4. H3BO3 - Boric Acid *1st dissociation only
5. C6H8O7 - Citric Acid
What is a BASE?
pH greater than 7 Feels slippery Dissolves fats and oils Usually forms OH- ions in
solution Neutralizes acids
Common Bases
NaOH- sodium hydroxide (LYE) soaps, drain cleaner
Mg (OH)2 - magnesium hydroxide-antacids Al(OH)3-aluminum hydroxide-antacids,
deodorants NH4OH-ammonium hydroxide- “ammonia”
Strong Bases
Strong Bases are Strong Electrolytes They dissociate completely in water. 100% of the BOH molecules break up into B+ and OH- ions.
There are eight common strong bases chemists MUST know:1. KOH - Potassium Hydroxide2. NaOH- Sodium Hydroxide3. LiOH - Lithium Hydroxide4. CsOH - Cesium Hydroxide5. RbOH- Rubidium Hydroxide6. Ba(OH)2 - Barium Hydroxide
7. Ca(OH)2 - Calcium Hydroxide
8. Sr(OH)2 - Strontium Hydroxide
Weak Bases
Weak Bases are Weak Electrolytes They DO NOT dissociate completely in water. 1% of the BOH molecules break up into B+ and OH- ions.
There are six common weak bases chemists MUST know:
1. NH3 - Ammonia
2. C5H5N - Pyridine
3. CH3NH2 - Methylamine
4. C3H5O2NH2 - Alanine
5. Be(OH)2 - Beryllium Hydroxide
6. Mg(OH)2 - Magnesium Hydroxide
Types of Acids and Bases
In the 1800’s chemical concepts were based on the reactions of aqueous solutions.
Svante Arrhenius developed a concept of acids and bases relevant to reactions in H2O.
Arrhenius acid – produces hydrogen ions in water.
Arrhenius base – produce hydroxide ions in water.
A broader ,more modern concept of acids and bases was developed later.
Bronsted-Lowry acid- donates a hydrogen ion in a reaction.
Bronsted – Lowry base – accepts a hydrogen in a reaction.
Conjugate acid- compound formed when an base gains a hydrogen ion.
Conjugate base – compound formed when an acid loses a hydrogen ion.
Another way to classify Acids and Bases
Acids can be classified by how many H+ ions per molecule are given.
Monoprotic acids Diprotic acids Polyprotic acids
Ex:H2SO4(aq) + H2O H3O+ + HSO4
-(aq)
HSO4- (aq) + H2O H3O+ + SO4
2-(aq)
Acid-Base Reactions Proton Transfer
This occurs in every acid-base reaction. When acids and bases react, a proton is
transferred from the acid to the base. This is the driving force of acid-base reactions. Once the proton is transferred, it is in a
position of less chemical potential. Formation of water
If the acid contains H+ and the base contains OH- the acid base reaction will form water.
The remaining cation and anion form a salt. If both the acid and base are weak, no
reaction occurs because no ions are present to initiate the proton transfer.
Acids and Bases in Solution
HCl + H20 H3O + + Cl- (more hydronium ions, more acidic)
NaOH in water Na+ + OH-
(more hydroxide ions, more basic) NaOH + HCl NaCl + HOH
Acid + Base yields type of salt and water
NH3 + H20 NH4+ + OH-
ammonia gas + water yields ammonium and hydroxide ions
Neutralization
Acid-Base Reactions are also called Neutralization Reactions
Acids and Bases are extremely corrosive materials. This means that they destroy things they come into
contact with, including skin, plant tissue, and even metals when the acid or base is strong enough.
For this reason, chemists should be VERY careful when handling them.
When acid-base reactions occur, corrosive materials become harmless materials (water and salt). Another way to say this is to say that they are
neutralized.
The Equations of a Strong Acid-Strong Base Reaction
Consider the reaction between nitric acid and potassium hydroxide.
Molecular EquationHNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)
Complete Ionic Equation – both acid & base dissociate.
H+(aq) + NO3-(aq) + K+(aq) + OH-(aq) K+(aq) + NO3
-(aq) + H2O(l)
Net Ionic Equation – always shows formation of water.
H+(aq) + OH-(aq) H2O(l)
The Equations of a Weak Acid-Strong Base Reaction
Consider the reaction between acetic acid and sodium hydroxide.
Molecular EquationHC2H3O2(aq) + NaOH(aq) NaC2H3O2 (aq) +
H2O(l)
Complete Ionic Equation – only the base dissociates.
HC2H3O2(aq) + Na+(aq) + OH-(aq) Na+(aq) + C2H3O2-(aq) + H2O(l)
Net Ionic EquationHC2H3O2(aq) + OH-(aq) H2O(l) + C2H3O2
-(aq)
The Equations of a Strong Acid-Weak Base Reaction
Consider the reaction between hydrochloric acid and ammonia.
Molecular EquationHCl(aq) + NH3 (aq) NH4
+(aq) + Cl-(aq)
Complete Ionic Equation – only the acid dissociates.
H+(aq) + Cl-(aq) + NH3(aq) NH4+(aq) + Cl-(aq)
Net Ionic EquationH+(aq) + NH3(aq) NH4
+(aq)
pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335
Reactions with indicators
Indicator Acid color
Neutral color
Base color
Phenolphthalein Colorless Faint pink Dark pink
Bromthymol blue
Yellow Green Blue
Litmus Red ----- Blue
pH paper
pH paper changes color to indicate a specific pH value.
Buffers
A buffer is a solution that resists changes in pH when small amounts of acids and bases are added.
Acids and Bases in Real LifeSituations in which pH is controlled
“Heartburn” Planting vegetables and flowers Fish Tanks and Ponds Blood Swimming pools
Acid Rain
Pollution in the air (sulfur dioxide, carbon dioxide, nitrogen dioxide) combines with water to form various acids.
.
Rapid changes in pH can kill fish and other organisms in lakes and streams.Soil pH is affected and can kill plants and create sinkholes
