Practicals

• Devise a plan that uses the reagents to unambiguously determine which solution is in which beaker. You should include the observations that enable you to positively identify all five solutions.

  1. Silver Nitrate to indentify halides
  2. Sodium Hydroxide to identify Barium compounds
  3. Sulfuric Acid to identify Magnesium compounds
  4. once compound identified no further reagents added to it
• titration [5]

  1. pipette 25cm3 of [solution] into conical flask
  2. add indicator to flask
  3. titrate with acid in burette until indicator just turns pale, ensuring to swirl mixture
  4. take readings on burette before and after titration
  5. subtract after from before to find titre used
• Outline a method to obtain pure dry crystals of ammonium sulfate by this procedure. [6]

  1. aqueous sulfuric acid in burette and record initial volume
  2. measure volume of ammonia into conical flask using pipette
  3. use indicator (NOT universal)
  4. titrate with aqueous sulfuric acid until colour of indicator just changes
  5. record final volume and repeat without using indicator
  6. concentrate neutralised solution
  7. leave to evaporate over time
  8. filter and dry crystals

  
• standard solution

  1. weigh accurately the required amount of []
  2. transfer [] to beaker and dissolve in small volume of deionised water, ensuring all dissolved
  3. transfer solution into volumetric flask with funnel
  4. wash out beaker with deionised water a few times, transfer washings to flask
  5. use Pasteur pipette to slowly add solvent until bottom of meniscus touches calibration mark
  6. stopper the volumetric flask and shake to ensure solution is thoroughly mixed
• obtain maximum of Magnesium Carbonate from known mass of Magnesium, two-stage process [6]

  1. addition of acid to form soluble salt
  2. excess acid to ensure maximum amount of Magnesium salt
  3. addition of soluble carbonate
  4. excess to ensure all Magnesium ions precipitate
  5. filter and dry precipitate
  6. equations
• A solution contains one cation and up to three different anions. The anions possibly present are carbonate, chloride and sulfate. Devise a plan that unambiguously proves which anions are present in the mixture. [6]

  carbonate

  1. add acid (not hydrochloric/sulfuric)
  2. effervescence
  3. add acid until no more fizzing
  4. divide solution into two

  sulfate

  1. add barium chloride to one half
  2. precipitate forms

  chloride

  1. add silver nitrate to other half
  2. precipitate forms
• Double titration


  1. Phenolphthalein - pH 9 + pink to colourless
  2. methyl orange - pH 4 + yellow to orange-pink
• do NOT use universal indicator in titrations


  only shows gradual change in colour as pH of solution changes