Transition Metals- Catalysts

• What do transition elements show?

  Variable oxidation states
• Which electrons do transition metals lose first when forming ions?

  4s electrons before 3d electrons
• What are the general trends in oxidation states of transition metals?

  • Relative stability of +2 state increases across the period
  • High oxidation state compounds are oxidising agents (e.g., MnO4-)
  • Low oxidation state compounds are reducing agents (e.g., V2+, Fe2+)
• What is the color of MnO4- in solution?

  Purple
• Why is the redox titration between Fe2+ and MnO4- self-indicating?

  Due to significant color change
• What is the balanced equation for the reaction between MnO4- and Fe2+?

  MnO4- + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+
• What acid is suitable for manganate titrations?

  Dilute sulfuric acid
• What happens if insufficient sulfuric acid is used in the titration?

  MnO2 is produced instead of Mn2+
• What effect does MnO2 have on the titration?

  It masks the color change
• Why can't concentrated HCl be used in manganate titrations?

  Cl- ions would be oxidized to Cl2
• What is the redox potential of MnO4-/Mn2+?

  +1.51 V
• What is the redox potential of Cl2/Cl-?

  +1.36 V
• Why can't nitric acid be used in manganate titrations?

  It is an oxidizing agent
• What are the oxidation states of vanadium and their corresponding colors?

  • VO2+ (oxidation state +5): yellow solution
  • VO2+ (oxidation state +4): blue solution
  • V3+ (oxidation state +3): green solution
  • V2+ (oxidation state +2): violet solution
• What happens when acid is added to solid VO3-?

  It turns into a yellow VO2+ solution
• What does zinc do to vanadium (V) in acidic solution?

  Reduces vanadium through oxidation states
• What is Tollens' reagent used for?

  Distinguishing between aldehydes and ketones
• What happens to silver in Tollens' reagent when aldehydes are present?

  Aldehydes reduce silver to metallic silver
• What influences the redox potential of transition metal ions?

  pH and the ligand
• What are the overall reactions for manganate titrations with hydrogen peroxide and ethanedioate?

  With hydrogen peroxide:

  • 2MnO4- + 6H+ + 5H2O2 → 5O2 + 2Mn2+ + 8H2O

  
  

  With ethanedioate:

  • 2MnO4- + 16H+ + 5C2O4^2- → 10CO2 + 2Mn2+ + 8H2O
• What is the reaction ratio between MnO4- and FeC2O4 in titrations?

  3 MnO4- to 5 FeC2O4
• Why is the reaction between MnO4- and C2O4^2- slow initially?

  Both are negative ions
• How do you calculate the percentage of iron by mass in a nail?

  Use titration data and mass of nail
• What is the first step in calculating the percentage of iron in the nail?

  Find moles of KMnO4 used
• How do you find the moles of KMnO4 used in the titration?

  moles = conc x vol
• What is the mass of Fe in the solution if 9.8 x 10^-3 mol of Fe2+ is present?

  0.547 g
• How do you calculate the percentage mass of iron in the nail?

  %mass = (mass of Fe / mass of nail) x 100
• What is the first step in calculating the percentage by mass of FeC2O4.2H2O in the original sample?

  Find moles of KMnO4 used
• How do you find the moles of FeC2O4.2H2O in 25 cm3?

  moles of KMnO4 x 5/3
• What is the final step to calculate the percentage by mass of FeC2O4.2H2O?

  %mass = (mass of FeC2O4.2H2O / mass of sample) x 100
• What are the steps to calculate the percentage by mass of FeC2O4.2H2O in a sample?

  1. Find moles of KMnO4 used
  2. Calculate moles of FeC2O4.2H2O in 25 cm3
  3. Scale up to find moles in 250 cm3
  4. Calculate mass of FeC2O4.2H2O
  5. Calculate % mass