The experiment is the mixing of hydrochloric acid and calcium hydroxide together and using an appropriate method to find the concentration of limewater.

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Chemistry Assessed Practical 2

Jared Ching

Planning:

Introduction and background:

        The experiment is the mixing of hydrochloric acid and calcium hydroxide together and using an appropriate method to find the concentration of limewater. This is the equation of the reaction:

Ca(OH)2(aq) +2HCl(l)           CaCl2(aq)+2H2O(l)

Knowing this and using calculations we can work out the concentration of limewater having titrated the two solutions, from the volumes and concentration of HCl. In the presence of Phenolphthalein hydroxides turn pink, when neutralized, go colourless, this will be the indication of the end of the reaction, when all limewater is reacted. However as stated in “Chemistry in context”, phenolphthalein has a very high end point to its pH scale, making it suitable for use in titrations with fairly high concentrations. But clearly using a weak base like calcium hydroxide would make methyl orange a better choice. Using phenolphthalein would change in colour before the point of balance between acid and base, thus giving inaccurate results.

        

Method:

        In order to find out concentration of the limewater, we need to dilute the hydrochloric acid to a very low concentration, so that it neutralizes the limewater slowly enough to record the change in volume of acid titrated. I predict that 0.02mol/dm3 solution of HCL acid will be sufficient as the limewater is stated to be around 1g/dm3 which is about 0.013mol/dm3. With the given solution of HCl, it is easily be diluted by adding water. Add exactly 25cm3 of HCl (using a glass pipette) to a 250cm3 volumetric flask then fill to the mark, then take exactly 25cm3 of this solution and dilute again in another identical flask to form the required concentration of 0.02mol/dm3. A control should also be made with excess HCl acid used to ensure that the end result colour is correct.

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        Thus we are set to carry out the experiment, using a regular titration set up, with the following method and apparatus:

Apparatus:

  • Volumetric flasks 250 cm3
  • Burette
  • Pipette 25cm3
  • Beakers
  • Chonical flasks 250 cm3
  • Retort stand and clamp
  • Methyl orange
  • Burette funnel
  • White tile
  • Provided solutions: 250cm3 limewater of 1g/dm3 and 2Mol solution HCl acid

Method break down:

        Having diluted the acid appropriately, prepare the equipment as follows:

  1. Clamp a burette to a retort stand securely, ensuring that the tap is closed
  2.  Pipette 25cm3 volume ...

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