Ox always change during redox reactions: - PowerPoint PPT Presentation

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Ox always change during redox reactions:

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Oxidation Numbers & Redox Reactions Ox always change during redox reactions: Increase Ox = Oxidation Decrease Ox = Reduction It s a redox reaction if: element ... – PowerPoint PPT presentation

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Title: Ox always change during redox reactions:


1
Oxidation Numbers Redox Reactions
  • Ox always change during redox reactions
  • Increase Ox Oxidation
  • Decrease Ox Reduction

Its a redox reaction if element ?
compound or compound ? element
S8(s) 8 O2(g) ? 8 SO2(g)
Ox(S) 0 ? 4 (oxidized lost e- increased
Ox) Ox(O) 0 ? -2 (reduced gained e-
decreased Ox)
2
Oxidation Numbers Redox Reactions
A more complex example
Cu is oxidized (Ox ? loss of e-). H is
unchanged. O is unchanged. N is reduced (Ox ?
gain of e-).
3
Oxidation Numbers Redox Reactions
Exchange reactions are not redox no change in
oxidation state occurs.
Pb(NO3)2(aq) 2 Kl(aq) ? 2 KNO3(aq) Pbl2(s)
4
Displacement Reactions
Redox
Fe(s) CuSO4(aq) ? FeSO4(aq) Cu(s) 0
2 2 0
Cu(s) 2 AgNO3(aq) ? Cu(NO3)2(aq) 2 Ag(s)
0 1 2 0
Not all metals can displace another from its
salts Cu(s) ZnSO4(aq) no reaction
An activity series was developed
5
Activity Series of Metals
Displace H2 from H2O (l), steam or acid
Displace H2 from steam or acid
Ease of oxidation decreases
Displace H2 from acid
No reaction with H2O, steam or acid
6
Displacement Reactions
  • Powerful reducing agents at the top.

Higher elements displace lower ones Zn(s)
CuSO4(aq) ? ZnSO4(aq) Cu(s) Mg(s) 2
HCl(aq) ? MgCl2(aq) H2(g)
  • Metals at the bottom are unreactive.
  • Coinage metals
  • Their ions are powerful oxidizing agents.

7
Displacement Reactions
8
Displacement Reactions
2 Na(s) 2 H2O(l) ? 2 NaOH(aq) H2(g)
9
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10
pH Scale
  • In pure water, a few molecules ionize to form
    H3O and OHH2O H2O ? OH H3O
  • In acidic and basic solutions, these
    concentrations are not equalacidic H3O gt
    OHbasic OH gt H3Oneutral H3O
    OH

11
pH Scale
  • Measure how much H3O is in a solution using pH
  • pH lt 7.0 acidic
  • pH gt 7.0 basic
  • pH 7.0 neutral
  • Measure of H3O and OH concentration (moles per
    liter) in a solution
  • As acidity increases, pH decreases

12
pH Scale
  • The pH scale is logarithmic100 102 log(102)
    210 101 log(101) 11 100 log(100)
    00.1 101 log(101) 10.01 102 log(102)
    2
  • pH log H3O
  • pH if H3O 105? 109? Acidic or basic?
  • pH if H3O 0.000057 M?

13
Finding H3O from pH
  • H3O 10-pH
  • What is H3O if pH 8.9?

14
pH Quantitative Measure of Acidity
  • Acidity is related to concentration of H (or
    H3O)
  • pH -logH3O
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