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With information about the molarity of both the diluted and concentrated HCl unknowns, the titration can be repeated more carefully.
Start by measuring out a second sample of sodium carbonate.
mass of sodium carbonate measured on an analytical balance
The results from the rough titration can be used to estimate how much volume will be needed to titrate a given mass of sodium carbonate. With a better idea of where the end point should be, HCl can be added quickly or continuously until the titration gets close to the end point (usually ~5 mL before the expected total volume needed), after which HCl can be added more slowly to ensure the titration does not overshoot the end point. Two common methods used to add titrant from a buret slowly are the half-twist method and the hanging drop method.
Half-twist Method
Half-twist Method
Quickly turn the stopcock 180°.
While the stopcock is being turned, a small amount of titrant will be dispensed.
Turning the stopcock faster will result in a smaller amount of titrant being dispensed per turn.
It is good practice to rinse the sides to ensure all titrant is absorbed into the analyte.
Hanging Drop Method
Hanging Drop Method
Turn the stopcock carefully until a drop of titrant forms at the tip.
After the drop starts to form, close the stopcock before the drop becomes large enough to fall from the tip.
Rinse the drop into the flask using distilled water from a wash bottle.
Rinse the sides of the flask to make sure all titrant is added into the analyte.
Initial volume of titrant read without a buret card
Initial volume of titrant read with a buret card
Final volume of titrant read without a buret card
Final volume of titrant read with a buret card
Analyte after titration
Using the buret readings and the mass of sodium carbonate, determine the molarity of the original concentrated solution. Your new value may vary from the one calculated from the rough titration due to experimental error of the rough titration and better technique used in the precise titration. Your calculations should give you a value of 5.04 M.
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