Acids & Bases
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Transcript of Acids & Bases
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Acids & Bases
Chemistry.Ms. Siddall.
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Standard 5a: Properties
Properties Acid Base
Taste Sour (lemon) Bitter (soap)
Touch Like water Like soap
Reaction with metal
Vigorous No reaction
Conductivity
Conducts electricity
Litmus Paper
Blue red Red blue
Neutralization
Acid + base salt + watere.x. HCl + NaOH NaCl +
H2O
e.x. HCl + Mg H2(g) + MgCl2
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Summary 1
1. Write the balanced equation for the reaction of aluminum with HCl to form hydrogen and aluminum chloride.
2. A substance turns red litmus blue and does not react with metal. What is it?
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Standard 5b: Brønsted-Lowry Definition
• Acids donate hydrogen ions(Hydrogen ion = H+ = proton)
e.x. HBr + H2O H3O+ + Br-
• Bases accept hydrogen ionse.x. NH3 + H2O NH4
+ + OH-
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Summary 2
• Write the balanced equation for the reaction of HF (hydrofluoric acid) with water.
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WeakAcidEquilibrium.exe
Strong acid ionization
weak acid ionization
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Standard 5c: Dissociation
• Acids:• Strong acid = strong electrolyte• Strong electrolyte = 100% dissociation
e.x. HNO3 + H2O H3O+ + NO3-
• in solution(H3O+ = hydronium ion)
• You MUST know these strong acids: HCl, HBr, HI, HNO3, H2SO4
0% 100%
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Summary 3
• Which of the following are strong acids? H2SO4, HSO3, HClO2, HBr, HNO3, HNO2
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Standard 5c: continued
• Weak acids = weak electrolytes• Weak electrolyte = Partial dissociation
(= equilibrium)
e.x. HCN + H2O H3O+ + CN-
• In solution• All other acids are weak acids
• Examples: acetic acid HC2H3O2, carbonic acid H2CO3, HCN, H3PO4
~97%
~3%
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Summary 4
• At equilibrium does a weak acid solution contain mostly products or mostly reactants?
• At equilibrium does a strong acid solution contain mostly products or mostly reactants?
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Standard 5c: continued
Conjugate acids & bases:e.x. HF + H2O H3O+ + F-
• acid– Donates hydrogen ion
• Conjugate base– Different from acid by a proton
• Base– Accepts hydrogen ion
• Conjugate acid – Different from base by a proton
A CBB CA
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Summary 5
• Label the acid (A), base (B), conjugate acid (ca), and conjugate base (cb) in the following reaction:
HNO3 + H2O H3O+ + NO3-
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Conjugate acids & base pairs:e.x. HF + H2O H3O+ + F-
• Acid and Conjugate base pair = HF & F-
• A strong acid has a weak conjugate base• A weak acid has a strong conjugate base
• Base and conjugate acid pair = H2O & H3O+
• A strong base has a weak conjugate acid• A weak base has a strong conjugate acid
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Summary 6
HF + H2O H3O+ + F-
1. Identify the acid and conjugate base. Label each as ‘weak’ or ‘strong’
2. Identify the base and conjugate acid. Label each as ‘weak’ or ‘strong’
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Standard 5d: pH scale
Definition:pH = -log[H3O+]
• pH measures the concentration (amount) of H3O+ ions in solution
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Summary 7
1. Write the equation for HCl reacting with water to make a hydronium ion and a chloride ion
2. Is the concentration of hydronium ions in this solution high or low?
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acidic
neutral
basic
pH0pH1pH2pH3pH4pH5pH6pH7pH8pH9pH10pH11pH12pH13pH14
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Summary 8
Provide an example of:1. An acidic compound2. A basic compound3. A neutral compound
Add a minimum of 3 acids and 3 bases to your pH scale
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Self ionization of pure waterH2O + H2O H3O+ + OH-
= Equilibrium system• For pure water: [H3O+] = [OH-] = 1x10-7M
• pH = -log[H3O+] = 7
• pH 7 = neutral• [H3O+] > [OH-] = pH < 7= acidic solution
• [H3O+] < [OH-] = pH > 7 = basic solution
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Summary 9
Identify the following solutions as acidic, basic, or neutral:
1. pH 32. pH 53. pH 104. pH 7
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Acids ‘produce’ H3O+ in solution
e.x. HCl + H2O H3O+ + Cl-
• pH measurement:[H3O+] = 0.1M = 1x10-1M
pH = -log [H3O+] = -log [1x10-1]
pH = 1
• High [H3O+] = ‘Low’ pH reading
= acidic solution
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Summary 10
1. pH measures the concentration of ___________________ ions in solution.
2. A solution with pH = 2:a) has a high / low concentration of
these ionsb) is acidic / basic
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Bases ‘decrease’ H3O+ in solution
e.x. NaOH + H3O+ Na+ + 2H2O
• pH measurement:[H3O+] = 1x10-14M
pH = -log [H3O+] = -log[1x10-14]
pH = 14
• Low [H3O+] = ‘High’ pH reading
= basic solution (Alkaline)
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Summary 11
1. What is the hydronium ion concentration for a solution with pH = 12?
2. Is the solution acidic or basic?
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5f: calculate pH
pH = -log[H3O+]
Example: [H3O+] = 4.5 x10-5M
• [H3O+] > 1x10-5M
• pH should be between 4 - 5• pH = -log[4.5x10-5] = 4.35
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Summary 13
• Estimate then calculate the pH for a solution with:
•[H3O+] = 7 x 10-2 M
•[H3O+] = 2.2 x 10-9 M
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pOH = -log[OH-] pOH + pH = 14
Example:• [OH-] = 1x10-2M• pOH = -log[1x10-2] = 2• pH = 14 - 2 = 12
Relationship between [OH-] and [H3O+]
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Summary 14
Complete the following table:
[H3O+] [OH-] pH pOH
10-5M
10-5M
1
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5e: acid/base definitions
Arrhenius: • acids are hydrogen containing
compounds that ionize to yield H+ ions in aqueous solution.
e.x. HCl(aq) H+(aq) + Cl-(aq)
• Bases ionize to yield OH- ions in aqueous solutions.
e.x. NaOH(aq) Na+(aq) + OH-
(aq)
• Problems: NH3 is not a base according to Arrhenius
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Summary 15
• Explain why NH3 is not a base according to the Arrhenius definition of a base.
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BrØnsted-Lowry:• Acid = hydrogen donor• Base = hydrogen acceptor
e.x. NH3(aq) +H2O NH4+ + OH-
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Lewis:• An acid accepts a pair of electrons
(accepts a negative charge)• Acid = proton donor = electron acceptor• A base donates a pair of electrons• Base = proton acceptor = electron
donoro e.x. HCl + H2O H3O+ + Cl-
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Electron acceptor
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Electron donor
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Summary 16
• Explain the difference between the Bronsted-Lowry definition and the Lewis definition of acids and bases
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5g: buffers
Buffer = a solution whose pH does not change (much) when acid or base are added.
• A buffer is a solution made from an acid and its conjugate base
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• Example: human blood must have a pH between 7.35 – 7.45 (or we will die)
• There are 2 buffer systems in human blood: H2PO4
-/HPO42- & H2CO3/HCO3
-
B- + H2PO4- HPO4
2- + HB
B- + H2CO3 HCO3- + HB
HB = acid (H+ donor)B- = base (H+ acceptor)
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Summary 17
•Write a general equation showing the buffering ability of HSO4
- and its conjugate base. (use B- as the base that reacts with HSO4
-)