Chemistry test 3

• Oxidation


  a chemical reaction in which a substance gains oxygen, or loses electrons
• Reduction

  when a substance loses oxygen, or gains electrons
• Oxidation

  • gain of oxygen
  • loss of hydrogen
  • loss of electrons
  • increase in oxidation number
• Reduction

  • loss of oxygen
  • gain of hydrogen
  • gain of electrons
  • decreases in oxidation number
• Redox Reaction

  oxidation and reduction always take place together
• Reduction Number Rules

  1. the oxidation number of an uncombined element is zero
  2. the oxidation number is usually given as a roman numeral
  3. the oxidation number of a single monatomic ion such as Mg is equal to the change of the ion
  4. transition elements have a variable oxidation number
  5. the sum of the oxidation number in the formula of a compound will equal to zero
• Oxidising Agent

  a substance that brings about the oxidation of another substance
• Reducing Agent


  a substance which brings about the reduction of another substance
• Conductors

  will allow electricity to flow through them
• Electrolyte

  is an ionic compound in the molter and aqueous state that conducts an electric current
• Non- Conductors ( insulators)


  will not allow electricity to flow through them
• Electrolysis

  is the deposition of an ionic compound when molten or in aqueous solutions
• Anode and Cathode

  • Anode - the positive electrode of a cell
  • Cathode - the negative electrode of an electrolysis cell
• Cathode & Anode

  
• Rules for electrolysis of a solution ( Cathode )

  1. If a metal is more reactive than hydrogen, its ions stay in solution and hydrogen bubbles off
  2. But if a metal is less reactive than hydrogen, the metal forms
• Rules for electrolysis of a solution ( Athode )

  1. If it's a concentrated solution of a halide then chlorine, bromine, or iodine solution forms
  2. But if the halide solution is dilute, or there is no halide, oxygen forms
• Order of Reactivity

  
• Electroplating

  Coating one metal with another using electrolysis

  Use: to prevent corrosion & approve the appearance
• Using Reductive Cu Electrodes

  • anode (orange) loses mass as it dissolves/corrodes
  • cathode (yellow) gains mass as Cu is deposited from the anode

  
• To Electroplate

  
• Endothermic Reactions

  • takes in thermal energy from surroundings
  • temp. from surroundings decreases
  • products have more energy than reactants
  • reactants + thermal energy -> products
• Exothermic Reactions

  • give out thermal energy to the surroundings
  • temp. of surroundings rises
  • products have less energy than resultants
  • reactants -> products + thermal energy
• Cathode Rules

  • The ion of the least reactive element will be discharged
  • Ex 1: If we have Mg & H, the H ions will be discharged
  • Ex 2: But if we have Cu & H, the Cu ions will be discharged ( Cu is less reactive than H)
• Anode Rules

  • If a halide is present ( F, Cl, Br, I ), they will be the one that gets discharged
  • If a halide isn't present, then its always the Hydroxide that gets discharged