The identity of the atom is determined by the

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• The identity of the atom is determined by the
  of protons in the nucleus.
• One can change one kind of atom into another by
  changing the number of protons in the nucleus
  These changes involve enormous amounts of energy.
  This is the source of nuclear energy and the
  atomic bomb.
• Most of these reactions result from nuclear decay
  and involve changes of only one or two protons in
  the nucleus.

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Can we turn copper into gold?

• On a Periodic Table the Atomic Number also tells
  us the number of protons in the nucleus.
• Copper has 29 protons in its nucleus.
• Gold has 79 protons in its nucleus
• Clearly we cant really turn copper into gold
• Alchemists didnt really have a prayer to
  actually convert a base metal into gold either.

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• Most chemical reactions occur from interactions
  of the electrons.
• A neutral atom has the same number of electrons
  as protons.
• However, an atom can gain and lose electrons
  fairly easily to form ions, which can have
  positive or negative charge.
• Electrons are also responsible for the forces
  (bonds) which hold atoms together in a molecule.

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• The majority of chemical reactions can be
  classified as one of two kind of major reaction
  types.
• Acid/Base Reactions
• Oxidation/Reduction (Redox) Reactions.

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The Proton

• The hydrogen atom has a mass of about 1 amu, as
  its nucleus contains only one proton and no
  neutrons. So the hydrogen atom without its
  electron has a charge of 1 and can be called a
  hydrogen ion, or more commonly a proton.

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Acid Base Reactions

• In an Acid Base reaction, the hydrogen ion is
  simply transferred from one molecule or ion to
  another molecule or ion.
• Any examples?

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This afternoons examples

• AcOH HCO3- ? AcO- H2CO3
• H2CO3 ? CO2 H2O
• This reaction is reversible so it is also true
  that
• CO2 H2O ?H2CO3 ? H HCO3-
• 2AcOH CaCO3 ?Ca(AcO)2 H2CO3
• H2CO3 ? CO2 H2O

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Oxidation-Reduction Reactions

• In a Redox reaction electrons are transferred
  from one atom, ion or molecule to another atom,
  ion or molecule.
• This is the reaction we will use to turn the
  copper penny into silver, or more accurately
  coat the penny with zinc.

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How does this happen?

• Zn(s) 4-OH ? ZnO22- 2 H2O 2e-
• 2H2O 2e- ? H2(g) 2OH-
• Zn(s) 2OH- ? H2(g) ZnO22-
• 2H2O ZnO2-? Zn2 4OH-
• Zn2 2e- ? Zn(s)
• 2OH- H2 ? 2H2O 2e-
• 2OH- H2 Zn2 ? Zn(s) 2H2O

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Silver Penny to Gold

• This process is neither acid/base nor redox.
• In this reaction we form an alloy, i.e. a metal
  mixture. When we heat the zinc coated penny, the
  zinc atoms mix with the copper atoms to form
  brass, which has a gold-like color.
• We can use colorless nail polish to prevent
  tarnishing. Real gold does not tarnish.

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What do we mean by tarnish?

• When a metal tarnishes, it is getting oxidized
  by O2 to a metal oxide.
• e.g. 4Ag O2 ? 2 Ag2O
• 2Zn O2 ? 2ZnO
• 2Cu O2 ? 2CuO
• Most metals, like these oxidize easily and form a
  smooth layer of oxides on the surface of the
  metal that actually protects it from further
  oxidation.

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Iron doesnt tarnish, it rusts and corrodes

• 4 Fe 3O2 ? 2 Fe2O3 (rust)
• The difference here is that rust does not form a
  smooth surface on Iron, it flakes off, exposes
  more metal surface to oxidation. We call this
  corrosion.

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How is this a redox reaction?

• 4 Fe 3O2 ? 2 Fe2O3 (rust)
• 4 Fe ? 4Fe3 12e- iron gets oxidized
• 3O2 12e- ? 6O2- oxygen gets reduced
• 4Fe3 6O2- ? 2 Fe2O3

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How does acid rain affect this?

• Iron needs water to get oxidized by air(O2). The
  water allows ions to move around, which is
  necessary for iron to corrode.
• Iron will not rust in anaerobic water.
• Iron will not rust in anhydrous air.
• Salt or acid, increase the rate of the redox
  process.

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Creating Acid Rain

• Real acid rain is caused by the reaction of water
  with Nitrogen and sulfur oxides formed from car
  exhaust and industrial waste.
• e.g. SO3 H2O ? H2SO4(sulfuric acid!)

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Making acid rain

• We will make fake acid rain, by first
  generating CO2, then bubbling it into water.
• AcOH HCO3- ? AcO- H2CO3
• H2CO3 ? CO2 H2O
• This reaction is reversible so it is also true
  that
• CO2 H2O ?H2CO3 ? H HCO3-