Post on 19-Feb-2016
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Properties
Both conduct electricity (electrolytes) because they break apart to some degree in water.Acids produce H+ (proton) in water.Bases produce OH- (hydroxide) in water.
Samples:Acids: vinegar(acetic acid), lactic acid in sour milk, citric acid, Bases: ammonia, lye (NaOH), Milk of Magnesia Mg(OH)2.
More on Acids
1. Sour taste. NEVER taste acids in lab situations.2. Change color of indicators.3. Some acids react with metals & release H2 gas.4. Acids react with bases to produce salt & water.
When neutralization occurs, #1.-#3 disappear.5. Conduct electric current.
Neutralization Reaction
Acid + Base --> Salt + WaterHCl + NaOH --> NaCl + H20H2SO4 + Ca(OH)2 --> CaSO4 + 2H20
Acid Nomenclature
• Binary Acids contain Hydrogen and another element:
• Hydro + root of 2nd element + ic– HF hydrofluoric acid– HCl hydrochloric acid– HBr hdrobromic acid– HI hydroiodic …– H2S hydrosulfuric …
Bases
• Bitter taste (NEVER taste bases in labs).• Change the color of indicators.• Slippery feel (dilute bases, don’t touch
concentrated bases)• React with acids to produce salt & water• Conduct electric current.
Arrhenius Acids & Bases
• Arrhenius Acid is a chemical compound that increases the concentration of hydrogen ions, H+, in aqueous solutions.
• Arrhenius Base is a chemical compound that increases the concentration of hydroxide ions, OH-, in aqueous solutions.
• When put with water, these compounds dissociate (break apart) forming ions
• HNO3 (l) + H20 (l) --> NO3- (aq) + H30+ (aq)
• When put in water, HNO3 , ionizes and the charged particles formed can conduct electricity.
• The amount of H30+ (hydronium) produced is an indication of the acid’s strength.
Strong Acids ionize completely in water.
Strong Acids:• HI• HClO4
• HBr• HCl• H2SO4
• HClO3
Weak Acide release few hydrogen ions in water.
Weak Acids:• HSO4
-
• H3PO4
• HF• CH3COOH
• H2CO3
• H2S• HCN• HCO3
-
For Bases, the strength depends on how it dissociates (ionizes)
Strong Bases ionize completely.
Strong Bases• Ca(OH)2 --> Ca2+ + 2OH-
• Sr(OH)2
• Ba(OH)2
• NaOH• KOH• RbOH• CsOH
Weal Bases ionize slightly.Weak Bases• NH3 + H2O NH4
+ + OH-
• C6H5NH2
“ “ means the reaction is
reversible
Acid-Base Theories
Bronsted-Lowry Acids donate protons (H+)Molecules or ions can donate protons.HCl + NH3 NH4
+ + Cl-
The HCl is a Bronsted-Lowry Acid. It donates a proton to water
Water can act as a Bronsted-Lowry Acid also as in the following reaction:
H2O (l) + NH3 OH- + NH4+
Bronsted-Lowry Bases
accept protons. In the equation below, ammonia is the base, because it accepts the proton to become an ammonium ion.
acid baseHCl + NH3 NH4
+ + Cl-
Mono- and Polyprotic Acids• Monoprotic acids can only donate one proton
per molecule. Ex.: HCl, HNO3
• Polyprotic acids can donate 2 or more protons per molecule. Ex.: H2SO4, H3PO4
• For polyprotic acids the donations occur in stages, losing one H+ at a time.
Lewis Acids and Bases
• Arrhenius and Bronsted-Lowery definitions have some limitations. Lewis classification is based on bonding and structure including substances without hydrogen. The Lewis classification is more complete than the other 2 methods.
A Lewis acid
is an atom, ion or molecule that accepts an electron pair to form a covalent bond.
Dot notation
Structural formula – a bar represents what?A pair of shared electrons.
Lewis Acid-Base Reaction• is the formation of one or more covalent
bonds between an electron-pair donor and an electron-pair acceptor.
Pair of donated electrons
491/15. Dilute HCl(aq) and KOH(aq) are mixed in chemically equivalent quantities.
a) Write the formula equation for the reaction.HCl(aq) + KOH(aq) --> KCl(aq) + H2O(l)b) Write the overall ionic equation.H3O+(aq) + Cl-(aq) + K+(aq) + OH-(aq) --> K+(aq) + Cl-(aq) + 2H20(l)c) Write the net ionic equation.H3O+(aq) + OH-(aq) --> 2H20(l)
492/17a. Write the formula equation and net ionic equation for this reaction.
Formula equation for: Zn(s) + HCl(aq) --> Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)Overall ionic equation:Zn(s) + 2H3O+(aq) + 2Cl-(aq) --> Zn2+(aq) + 2Cl-(aq) + H2(g) + 2H20(l)Net ionic equation:Zn(s) + 2H30+(aq) --> Zn2+(aq) + H2(g) + 2H20(l)
Acid-Base Reactions
• Now we are going to use Bronsted-Lowry description to explore acid-base reactions.
• What was the Bronsted-Lowery theory?• B-L acid donates protons• B-L base accepts protons
• A conjugate base is the species that remains after a Bronsted-Lowery acid has given up a proton.
• A conjugate acid is the species that forms when a Bronsted-Lowery base gains a proton.
Acid-Base Reactions
Now we are going to use Bronsted-Lowry definitions to study Acid-Base reactions.
The species that remains after a Bronsted-Lowry acid has given up a proton is the conjugate base of that acid.
HF + H2O F- + H30+
Acid conjugate base
The species that is formed when a Bronsted-Lowry base gains a proton is the conjugate acid of that base.
HF(aq) + H2O(l) F-(aq) + H30+(aq) Base conjugate acid
HF(aq) + H2O(l) F-(aq) + H30+(aq) Acid Base conjugate conjugate
base acid acid1 base2 base1 acid2
Conjugate pairs: (1) HF and F- (2) H20 and H30+
Strength of Conjugate Acids & Bases
• On Page 1 of your handout for this chapter, you have a table which lists and compares the strengths of various acids and their conjugate bases. Get your Ch. 14 handout out now.
Determining direction of equilibrium in Acid-Base reactions
The stronger an acid is, the weaker its conjugate base will be.
The stronger a base is, the weaker its conjugate acid will be.
From these concepts, we can predict the outcome of a reaction.
Assignment for this section:#74: 489/1,2#77: 491/19-25#78: 492/26-30,36,37 (Overall practice problems)
Sample problem on next page:
492/23a: Identify the proton donor or acid and the proton acceptor or base. Label each acid-
base conjugate pair.CH3COOH + H20 H30+ + CH3COO-
acid base conjugate conjugate acid base
Another sample.
492/29a. Write the formula equation, the overall ionic equation, and the net ionic equation for a neutralization reaction that would form RbClO4.
Formula equation:RbOH(aq) + HClO4(aq) --> RbClO4(aq) + H20(l)
Overall Ionic equation:Rb+(aq) + OH-(aq) + H30+(aq) + ClO4
-(aq) --> Rb+(aq) + ClO4
-(aq) + 2H20(l)Net ionic equation:H30+(aq) + OH-(aq) --> 2H20(l)
Amphoteric Compounds
These can act as either an acid or a base.Water acts as a base in this reaction:H2SO4(aq) + H20(l) --> H30+(aq) + HSO4
-(aq) acid1 base2 acid2 base1
But, water acts as an acid here:NH3(g) + H20(l) NH4
+(aq) + OH-(aq)Base1 acid2 acid1 base2