PRACTICALS

• appartus to measure volume : gas syringe 1dm3
• If at room temperature we use the v = n x 24dm3 or 24000 cm3 equation

  
• To accurately measure mass we use a digital balance that records masses to larger divisions
• We must add the bung quickly to the gas syringe to ensure no gases are lost to the surroundings
• Sources of error regarding volume of gas produced : some gas may have been released to the surroundings , reaction may be incomplete , some gas may have dissolved in water meaning a smaller volume of gas is collected
• 1. In an Acid base titration use a pipette to add 25cm3 of acid to the conical flask . Us an indicator
  2. pour alkali into burette or vice versa
  3. Conical flask needs to swirled above a white tile stop adding as soon as endpoint is reached
  4. repeat to find 2 Concordant results
• Use distilled water to create washing’s from the solution
• Accuracy of volumetric flask : fill the bottom of the meniscus on the graduation line
• Standard solution - a solution of known concentration
• Standard solution steps

  1. weigh out a substance
  2. add a small volume of distilled water
  3. fill in 250cm3 volumetric flask
  4. add all the Washings the flask
  5. fill to the graduation line and then invert the flask
• Indicators : methyl orange and phenalphalien
• Concordant results : titres that are within 0.1Cm3 of eachother
• Accurate burette readings

  1. read from the bottom of the meniscus
  2. ensure there are no air bubbles
• A larger titre Volume gives a smaller percentage error
• A smaller concentration gives rise to a larger titre which then allows for a smaller % error
• We carry trial titres in order to estimate the titre
• purification stages : use separating funnel to remove organic and aqueous layer , anhydrous salt to dry organic layer and redistill at a given temperature
• To speed up any chemical reaction we Can increase the temperature this could be done by adding test tubes in a water bath
• Anti bumping granules : prevent large numbers of bubbles forming and ensures liquid does not overboil
• Some gas may have escaped before putting the bung on

  
• Iodine clock errors : inaccurate timing of colour change due to eyesight being subjective . We should calculate average value form 2 students
• to test for iodine we use starch it should change from blue-black yo colourless
• if a solution is not in excess the mass would be lower due to a smaller titre
• if burette readings are read from the top of the meniscus the mass provided will still be the same as burette measures by difference
• increase accuracy of an experiment : repeat titrations to find concordant results , measure volume up to 250cm3 with volumetric flask