Determining the concentration of a limewater solution by volumetric analysis Essay Example

into the volumetric flask.

Fill this flask up to 250cm3 with distilled H2O by using the 5cm3 pipette when nearing the 250 mark for accuracy. Shake the flask well and now the hydrochloric acid in this flask is 0.2mol dm-3 (as 25cm3/250cm3=0.1. 0.

1�2.00mol dm3=0.20mol dm-3).The next step is the titration and the following equipment is needed:* a 25cm3 pipette with pipette filler to collect a dose of hydrochloric acid* A 250cm3 conical flask to contain the limewater to titrate hydrochloric acid into* a clear sheet of white paper to make noticing colour changes of the indicator more prominent* a 50cm3 burette and burette stand which is essential titrate from and measure the titration* a funnel to prevent spillages when adding dilute hydrochloric acid to the burette* another 25cm3 pipette with filler to collect accurate and measured amounts of limewater for numerous titrations* limewater* and phenolphthalein to provide a visual indicator of the endpoint.

I have chosen phenolphthalein as my indicator over methyl orange as the colour change is more prominent (turning from purple to colourless instead of yellow to red) but more importantly because the acid will be diluted and therefore weak and the pH of the final solution will be nearer to seven and this indicator has an end point closer to seven2 than methyl orange.Set up the burette to the stand and making sure the tap is closed, fill the burette to the 0.0cm3 mark. Do this using a funnel2 to prevent spillage but remember to remove this funnel afterwards as excess drips could ruin readings if left in the burette and ensure there is no air bubble at the tip of the burette1

that will make it seem there is more acid in the burette than there actually is.Now prepare the limewater; first shake the bottle of the limewater so the calcium hydroxide isn't all sitting at the bottom and then using the clean 25cm3 pipette take 25cm3 of limewater and eject it into the 250cm3 conical flask.

Make sure to have all the contents of the pipette by dipping the tip into the limewater solution. Now add no more than two drops of phenolphthalein into the solution as adding too much may affect the results1 (phenolphthalein is slightly acidic).Place the conical flask under the burette with the end in the flask1 (but not touching the solution) and carefully and slowly release the hydrochloric acid from the tap. Do this while swilling the conical flask to get a quicker colour change and not overshoot the acid.

Start releasing the acid in single drops when the purple solution in the flask begins to turn colourless and when the solution is completely colourless stop adding hydrochloric acid as the endpoint has been reached.Using this first attempt as a test run to get used to the procedure and be able to anticipate when the titration is reaching endpoint, analyse another 25cm3 of limewater by taking where the previous titration finished as the start point. Then repeat the titration again and again until at least three results3 are within 0.1cm3 of each other for reliability.