Unit 5 Tests

• Anions


  Negative ions
• Test for carbonate ions, CO3^2-


  1. Add strong acid to the sample

  2. Collect the gas produced

  3. Pass through lime water
• Observations for positive test of carbonate ions, CO3^2-
• Equation for carbonate ion test


  CO3^2- (aq) + 2H+ (aq) → H2O (aq) + CO2 (g)
• Test for sulfate ions, SO4^2-


  Add dilute hydrochloric acid and barium chloride to the sample
• Observations for positive test of sulfate ions, SO4^2-
• Equation for sulfate ion test


  Ba2+ (aq) + SO4^2- (aq) → BaSO4 (s)
• Reagent used to test for halide ions


  Acidified AgNO3
• Why HNO3 is used instead of HCl to test for halides
• How to test for a halide ion

  Dissolve the sample in water

  Add aqueous silver nitrate

  Record the colour change

  If difficult to distinguish the colour, add aqueous ammonia, first dilute ammonia then concentrated ammonia

  Note the solubility of precipitate
• Order of tests for carbonate, sulfate and halide ions
• Cations


  Positive ions
• Test for ammonium ions, NH4+

  Add sodium hydroxide to the sample and warm it

  Test the gas produced with red litmus paper
• Equation for ammonium ions test

  NH4+ (aq) + OH- (aq) → NH3 (aq) + H2O (aq)
• Reactions of aqueous cations

  • aluminium, Al 3+(aq)
  • ammonium, NH4+(aq)
  • barium, Ba2+(aq)
  • calcium, Ca2+(aq)
  • chromium(III), Cr3+(aq)
  • copper(II), Cu2+(aq)
  • iron(II), Fe2+(aq)
  • iron(III), Fe3+(aq)
  • magnesium, Mg2+(aq)
  • manganese(II), Mn2+(aq)
  • zinc, Zn2+(aq)
• Carbonate, CO32–


  CO2 liberated by dilute acids
• Chloride, Cl–(aq)


  Gives white ppt. with Ag+(aq) (soluble in NH3(aq))
• Bromide, Br–(aq)


  Gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq))
• Iodide, I–(aq)


  Gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq))
• Nitrate, NO3–(aq)


  NH3 liberated on heating with OH–(aq) and Al foil
• Nitrite, NO2–(aq)


  NH3 liberated on heating with OH–(aq) and Al foil
• Sulfate, SO42–(aq)


  Gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids)
• Sulfite, SO32–(aq)


  Gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids)
• Ammonia, NH3


  Turns damp red litmus paper blue
• Carbon dioxide, CO2


  Gives a white ppt. with limewater (ppt. dissolves with excess CO2)
• Chlorine, Cl2


  Bleaches damp litmus paper
• Hydrogen, H2


  'Pops' with a lighted splint
• Oxygen, O2


  Relights a glowing splint
• Aluminium in NaOH (aq)

  White ppt, Soluable in excess
• Aluminium in NH3 (AQ)

  White ppt, Insoluable in excess
• NH4+ - Ammonium in NAoH (aq)


  no ppt, Ammmonia NH3 produced on heating
• NH4+ - Ammonium in NH3


  No reaction
• Ba2+ - Barium in NaOh(aq)


  Faint white ppt unless pure
• Ba2+ - Barium in NH3


  no ppt
• Ca2+ - Calcium in NaOh(aq)


  white ppt in high conc of Ca2+OH
• Ca2+ - Calcium in Nh3(aq)


  no ppt
• Cr3+ - Chromium (III) in NaOh(aq)


  green-grey ppt , soluable in excess
• Cr3+ - Chromium (III) in NH3


  green-grey ppt, insoluable in excess
• Cu2+ - Copper (II) in NaOH(aq)


  pale blue ppt, insoluable in excess
• Cu2+ - Copper (II) in NH3 (aq)


  bleu ppt , dark blue + soluable in excess