1 / 11

UNIT 5

UNIT 5. Aqueous Reactions and Solution Stoichiometry Redox Reactions. Redox Reactions. Redox is short for “ oxidation-reduction .” Plating and combustion are redox reactions. Consider the following redox reaction: Fe (s) + Ni(NO 3 ) 2 (aq)  Fe(NO 3 ) 2 (aq) + Ni (s). O xidation

xena
Télécharger la présentation

UNIT 5

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UNIT 5 Aqueous Reactions and Solution Stoichiometry Redox Reactions

  2. Redox Reactions • Redox is short for “oxidation-reduction.” • Plating and combustion are redox reactions. • Consider the following redox reaction: • Fe (s) + Ni(NO3)2 (aq) Fe(NO3)2(aq) + Ni (s) Oxidation Is Loss of electrons Reduction Is Gain of electrons • Fe goes from an element to an ion: Fe  Fe2+ • Fe got oxidized • Ni goes from an ion to an element: Ni2+  Ni • Ni2+ gotreduced

  3. Oxidation Numbers We determine whether a chemical species has been oxidized or reduced by looking at the change in its oxidation number. Fe (s) + Ni(NO3)2 (aq) Fe(NO3)2(aq) + Ni (s) ox # 0 +2 +2 0 • The oxidation number of an element is 0. • The oxidation number of a monatomic ion is its charge. • The ox # for Fe went up. It was oxidized. • The ox # for Ni2+ went down. It was reduced (reduced = down). Oxidation Is Loss of electrons Reduction Is Gain of electrons

  4. Oxidation Numbers - Rules • The oxidation number of an element is 0. • The oxidation number of a monatomic ion is its charge. • The oxidation number of oxygen in a compound is usually -2 (exception is peroxide, O22-, where the oxidation number is -1). • The oxidation number of hydrogen in a compound is 1 when bonded to nonmetals and -1 when bonded to metals. • The oxidation number of fluoride is always -1. • The sum of the oxidation numbers in a neutral compound is zero. • The sum of the oxidation numbers in a polyatomic ion is the charge of the ion.

  5. Oxidation Numbers - Examples Species oxidation Species oxidation number number Fe Na+ H2 H+ O2 O2- Al3+ Cl- Fe2+ N3- S in SO42- : Cr in Cr2O72- N in NO3- S in SO32- N in NO2- P in PO43- C in CO32- 0 0 0 +3 +2 +1 +1 -2 -1 -3 overall charge of ion is -2 = ox # of S + 4(ox # of O) -2 = ox # of S + 4(-2) -2 = ox # of S – 8 -2+8 = 6 = ox # of S +6 +4 +5 +5 +3 +4

  6. Redox Reactions To see if a redox reaction has occurred, check to see if the oxidation numbers of any element involved in the reaction have changed. Mg (s) + Fe(NO3)2 (aq) Mg(NO3)2(aq) + Fe (s) ox #0 +2 +5 -2 +2 +5 -2 0 • Mg goes from an element to an ion: Mg  Mg2+ • Mg gotoxidized. Fe2+ was the oxidizing agent. • Fe goes from an ion to an element: Fe2+  Fe • Fe2+ gotreduced. Mg was the reducing agent. • This type of redox reaction, where the ion in solution is replaced through the oxidation of an element, is called a single replacement reaction. Oxidation Is Loss of electrons Reduction Is Gain of electrons

  7. Redox Reactions • Single replacement reactions have the form: • A + BX (aq)  AX (aq) + B • Single replacement reactions will occur if the element A is more likely to get oxidized than the ion B. • The activity series gives this information. See the table in the text. Oxidation Is Loss of electrons Reduction Is Gain of electrons • Notice that H2 (g) is included in this series. The series can tell us whether a metal will dissolve in acid.

  8. Will the following pairs react? Zn + Cu(NO3)2 (aq) Cu + Zn(NO3)2 (aq) Zn + NaNO3 (aq) Au + AgNO3 (aq) Ag + Au(NO3)3 (aq) Will the following metals dissolve in acid? Li Al Ni Cu Au What gas will be produced? H2 y n n n y y y y n n

  9. Redox Reactions - Examples Molecular equation: Mg (s) + Fe(NO3)2 (aq) Mg(NO3)2(aq) + Fe (s) Net Ionic equation: Mg (s) + Fe2+ (aq) Mg2+(aq) + Fe (s) Mg got oxidized. Fe2+ was the oxidizing agent. Fe2+ got reduced. Mg was the reducing agent.

  10. Redox Reactions - Examples When Zn dissolves in sulfuric acid, themolecular equationis Zn (s) + H2SO4 (aq) ZnSO4(aq) + H2 (g), thetotal ionic equationis Zn(s) + 2H+(aq) + SO42-(aq) Zn2+(aq) + SO42-(aq) + H2 (g), and thenet ionic equationis: Zn(s) + 2H+(aq) Zn2+(aq) + H2 (g) Zn got oxidized. H+ was the oxidizing agent. H+ got reduced. Zn was the reducing agent.

  11. Summary of Reactions • Combination A + B  AB • Decomposition AB  A + B • Metathesis AX + BY  AY + BX • acid-base neutralization • (example) HCl + NaOH  H2O + NaCl • Redox (example) Fe(s) + Ni2+ Fe2+ + Ni(s) • combustion • (example) CH2O + O2 CO2 +H2O • single replacement • (example) 2Na(s) + 2H2O  2NaOH + H2(g)

More Related