CP3 - Titration

• how can you calibrate the pipette and burette

  ensure there are no air bubbles
• concordant results

  results with 0.2 cm3 of each other

  should be the only ones used when calculating the mean titre
• why is it better to swirl the conical flask

  to ensure all the acid reacts with the alkali
• why might phenolphthalein turn colourless at the end point if you leave solution to stand and how may this affect the concentration and volume of sodium hydroxide needed

  sodium hydroxide reacts with carbon dioxide from air to form sodium carbonate

  this will make the concentration of NaOH decrease but volume needed to reach the end point won't change because Na2CO3 still reacts with HCl in the same ratio as NaOH
• risk assessment


  hydrochloric acid: irritant so auses severe burns and eye damage

  sodium hydroxide: corrosive and irritant so can cause skin burns and eye damage

  phenolphthalein: Flammable and toxic so can rapidly spread fire and irritate skin
• risk assessment-precautions

  hydrochloric acid: wear goggles, avoid contact with skin, keep container lids tightly closed

  sodium hydroxide: clean any spills immediately with paper to towels, avoid contact with skin, wear goggles

  phenolphthalein: keep away from open flames, wear goggles