gravimetric analysis

• What is gravimetric analysis?


  It determines mass or concentration by mass change
• What is the concentration of the AgNO3 solution used in gravimetric analysis?

  0.5 mol dm‒3
• What is the concentration of the HNO3 solution used in gravimetric analysis?

  1. 0 mol dm‒3
• What is the concentration of the HCl solution used in gravimetric analysis?

  1. 0 mol dm‒3
• What are the hazards associated with AgNO3?

  AgNO3 is corrosive
• What are the hazards associated with HNO3?

  HNO3 is corrosive
• What are the hazards associated with HCl?

  HCl is an irritant
• What is the method to identify an unknown metal chloride using gravimetric analysis?

  1. Weigh 0.3 g of unknown chloride.
  2. Dissolve in 100 cm³ deionised water with 3 cm³ HNO3.
  3. Add 20 cm³ AgNO3 until gel forms, then 5 cm³ more.
  4. Heat for 10 minutes without boiling.
  5. Cool for 2 hours.
  6. Weigh filter paper and place in funnel.
  7. Pour mixture into funnel, wash with 3 cm³ wash solution.
  8. Transfer precipitate to funnel, wash with 20 cm³ wash solution.
  9. Test wash solution with HCl; rewash if precipitate forms.

  10. Dry precipitate at 105 °C until constant mass.
• What is the filtrate in filtration?

  The solution passing through the filter paper
• What is the residue in filtration?

  The solid collected on the filter paper
• Why is filtration used in gravimetric analysis of a metal chloride?

  To separate silver chloride precipitate from solution
• Why is the filter paper weighed before use?

  To calculate the mass of solid accurately
• Why should the solution not be allowed to boil in gravimetric analysis?

  Evaporation may cause product loss
• Why are washings used in gravimetric analysis?

  To remove all precipitate from the beaker
• Why is deionised water used as a wash solution?

  It does not interfere with reactions
• Why is HNO3 diluted into the wash solution?

  To react with ions that may precipitate
• Why is the used wash solution tested with HCl?

  To check for unreacted silver ions
• Why is the solution re-filtered if a white precipitate forms with HCl?

  To collect remaining silver chloride
• Why is a final filtrate dried until constant mass?

  To ensure all water has evaporated
• What is the ionic equation for the reaction between silver nitrate and the unknown metal chloride?

  Ag+(aq) + Cl-(aq) → AgCl(s)
• What causes the white precipitate in gravimetric analysis?

  Silver chloride (AgCl)
• Why is HNO3 added to a chloride solution before AgNO3?

  To react with interfering ions
• Why is the reaction mixture heated before filtering?

  To coagulate silver chloride particles
• Why is the reaction mixture left to stand for two hours?

  To allow silver chloride to fully coagulate
• How do you calculate the mass of the dried solid collected on the filter paper?

  Mass of solid = final mass - initial mass