chapter 10 acids and bases
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Chapter 10 Acids and Bases. (10.1) Acid-Base Strength. Strong Acid (SA). an acid that dissociates completely into ions in water Ex.)all molecules of HCl (aq) dissociate into H + and Cl - ions the H + ions that are formed bond with H 2 O to form H 3 O + - PowerPoint PPT PresentationTRANSCRIPT
Chapter 10Acids and Bases
(10.1) Acid-Base Strength
Strong Acid (SA)
• an acid that dissociates completely into ions in water• Ex.)all molecules of HCl(aq) dissociate into
H+ and Cl- ions• the H+ ions that are formed bond with H2O to form
H3O+
HCl(aq) + H2O(l) H3O+(aq) + Cl-
(aq)
Strong Acid (SA)
other SA’s are…..HBrHIHNO3
H2SO4
HClO4
Concentration
• the conc. of H3O+(aq) ions, [H3O+], in a dilute
solution of a SA is equal to the conc. of the acid, [acid]
[H3O+] = [strong acid]
• Ex.) In a sample of 1.0 mol/L HCl(aq)
[H3O+] = 1.0 mol/L
square bracketMolar Concentration
Recall: C = n V
Dissociation (Strong Acid)
Text p 381 Figure 10.6100% of hydrogen chloride molecules dissociate
Dissociation (Weak Acid)Text p 382 Figure 10.71% of acetic acid molecules dissociate. In solution
there are mostly acetic acid molecules and only some ions.
Weak Acid (WA)
• an acid that dissociates very slightly into ions in water
• Ex.) not all molecules of CH3COOH(aq) break apart, some remain intact
• only about 1% of acetic acid molecules dissociate• In a sample of 1.0 mol/L CH3COOH (aq) ,
[H3O+] <<< 1.0 mol/L
• That is, [H3O+] < [weak acid]
Strong Base (SB)
• a base that dissociates completely into ions in water
• Ex.) all molecules of NaOH(aq) dissociate into Na+ and OH- ions
• other SB’s are… KOHCa(OH)2
Ba(OH)2
Concentration
• the conc. of OH1-(aq) ions, [OH1-], in a dilute
solution of a SB is equal to the conc. of the base, [base]
[OH1-] = [strong base]• Ex.) In a sample of 1.0 mol/L NaOH(aq)
[OH1-] = 1.0 mol/L
Weak Base (WB)
• most bases are weak• WB dissociates very slightly into ions in
water• Ex.) ammonia
[OH1-] < [weak base]
Acid Dissociation
• few acids contain only a single H+ ion• monoprotic acid: produces one H+ ion • Ex.) HF(aq) + H2O(l) H3O+
(aq) + F-(aq)
(simplified) HF(aq) H+(aq) + F-
(aq)
Acid Dissociation
• many acids contain 2 or more H+ ions• diprotic acid: produces two H+ ions• Ex.) H2SO4 (aq) H+
(aq) + HSO4-(aq)
HSO4-(aq) H+
(aq) + SO42-
(aq)
H2SO4(aq) 2H+(aq) + SO4
2-(aq)
Acid Dissociation
• triprotic acid: produces three H+ ions• Ex.) H3PO4 (aq) H+
(aq) + H2PO4-(aq)
H2PO4-(aq) H+
(aq) + HPO42-
(aq)
HPO42-
(aq) H+(aq) + PO4
3-(aq)
H3PO4(aq) 3 H+(aq) + PO4
3-(aq)
Measuring Strength – pH Scale
• In pure water, [H3O+] = [OH-] = 1.0 x 10-7 mol/L
• In acidic sol’n, [H3O+] > [OH-]
• In basic sol’n, [H3O+] < [OH-]
Measuring Strength – pH Scale
• In any aqueous sol’n the product can be calculated,
[H3O+] x [OH-] = 1.0 x 10-14
• The values of [H3O+] range from 10 mol/L to 10-15 mol/L
pH Scale
• We use system of logarithms to handle the range of exponents for [H3O+]
• Ex.) log (1x102) = 2log (1x10-6)= - 6
• simply, use the exponent when the value is written as 1 x base 10
or • use your calculator
pH Scale
• Ex.) [H3O+(aq)] = 1.0 x10-4
pH = -log[1.0 x10-4]= +4
pH = -log[H3O+(aq)]
pH Scale
Calculate,1)pH if [H3O+
(aq)] = 3.8 x10-3 mol/L
(ans: 2.42)2) [H3O+
(aq)] if pH = 3.85
(ans: 1.4 x 10-4 mol/L)3) pH of 0.082 mol/L HCl(aq)
(ans: 1.09)
[H3O+(aq)] = 10-pH
pOH Scale
• Ex.) [OH-(aq)] = 1.0 x10-6
pH = -log[1.0 x10-6]= +6
pOH = -log[OH-(aq)]
pOH + pH = 14
Homework