titration practical

• Titration:

  An experimental technique used to find an unknown concentration of an acid or an alkali.

  
• Titration equipment:

  A) burette

  B) pipette

  C) conical flask

  D) white tile

  
• Pipette:

  • To accurately measure a certain volume of acid or alkali (normally 25 cm3).

  Conical flask:

  • To contain the liquid from the pipette.

  
• Burette:

  • To add alkali or acid to the the conical flask.

  White tile:

  • To place the conical flask on.

  
• • Use a pipette to add 25 cm3 of alkali to a conical flask
  • Add a drops of indicator
  • Put the conical flask on a white tile
  • Fill the burette with acid
  • Note the starting volume
  • Add the acid from the burette to the alkali in the conical flask, swirling to mix
  • Stop adding the acid when the end-point is reached
  • (when the acid has neutralised the alkali & the indicator changes colour)
  • Note the final volume reading
  • Calculate how much acid you added in total
  • Repeat the titration until you get concordant results
  • Use results to calculate the mean volume of acid required to neutralise the alkali

  
• concordant results:


  Volumes of acid that are within 0.10 cm3 of each other.

  
• Indicators:


  Changes colour as the pH changes from acidic to alkaline.
• In titrations:

  • You can add acid from the burette to an alkali in the flask.
  • You can also do acid in the flask & the alkali in the burette.

  
• When doing a titration:

  • Place an indicator in the conical flask to tell when the acid has neutralised the alkali.
  • Swirl the conical flask as you add the acid from the burette in order to evenly distribute it.
  • Ensure that the colour change occurs as soon as neutralisation takes place.
  • Place the conical flask on a white tile to see when the colour change takes place more easily.

  
• Always add the indicator to the flask (not the burette).

  • So you may need to use a different indicator, whether it's an alkali or acid in the flask.

  There's 3 different type of indicators & their respective colour changes) you should know:

  • Litmus
  • Phenolphthalein
  • Methyl orange

  
• Litmus:


  An indicator that's red in acidic solutions & blue in alkaline solutions.

  
• Phenolphthalein:


  An indicator that's colourless in acidic solutions & pink in alkaline solutions.

  
• Methyl orange:


  An indicator that's red in acidic solutions & yellow in alkaline solutions.

  
• A pipette should be used to accurately measure the volume of the acid or alkali before transferring it to a conical flask.

  
• 1cm = 1000dm
• To convert concentration from mol/dm3 to g/dm3, multiply the concentration in mol/dm3 by its relative formula mass.
• Number of moles of gas = volume / 24dm3
• • Concentration (mol/dm3) = number of moles ÷ volume (dm3)
• • Number of moles of liquid = concentration (mol/dm3) x volume (dm3)
• • volume (dm3) = number of moles / concentration (mol/dm3)
• CONCENTRATION:


  The AMOUNT OF A SUBSTANCE within a certain VOLUME of solution. 

  • The more SOLUTE there is in a given volume, the more concentrated the solution is.
• Volume can be measured in cm3 or dm3. 

  • You can CONVERT between the two by multiplying & dividing by 1000
  • Concentration is typically measured in grams per decimetre cubed (g/dm³).

  
• Concentration (g/dm^3) = Mass (g) / volume (dm3)
• Mass (g) = Concentration (g/dm^3) x volume (dm3)
• Volume (dm3) = Mass (g) / Concentration (g/dm^3)
• number of moles of solid = mass / RFM
• • as the mass of acid dissolved is doubles & the volume of the solution is halved
  • the concentration of an acid increases