RP1 - preparing a volumetric solution

Describe how you could accurately measure the volume in a burette

Read from the bottom of the meniscus line and a piece of paper held behind the burette can cast a shadow on the meniscus making it easier to read

Explain how the use of a burette in this procedure contributes to the precision of the titre value

The uncertainty of the apparatus is smaller than other equipment e.g. measuring cylinder

What effect does adding water to the conical flask have on the titre

• There is no effect on the titre

• Although the conical flask solution will become more dilute, the moles of the reagent are the same and therefore the titre will be the same

• Due to the fact that the number of moles of each reagent that are needed to cause a colour change in the indicator is the same, whatever the volume of the solution is 

Explain why concordant results are used to calculate the mean titre

Concordant results are within 0.1cm3 of each other and are therefore more likely to be reliable

Explain why it is important to rinse out the conical flask with distilled water before it is used in the titration

• The pipette is used to transfer a certain number of moles of standard solution into the conical flask

• Rinsing the conical flask beforehand with anything other than distilled water will add to this number of moles and lead to an inaccurate result

Explain the effect on the titre value if the funnel was left in the top of the burette during the titration

• Titre may be slightly lower

• Because drips of the reagent could drip into the burette and increase the volume slightly

Explain the effect on the titre if there was an air bubble in the spout of the burrete during the titration

• Titre value may by slightly higher than an accurate measurement

• Volume in the burette would decrease as the air bubble was released but no reagent would have been added

Describe 5 steps taken during the titration to ensure that accurate results are obtained

• Put a white tile underneath the conical flask to see end point better

• Remove funnel from burette before titrating

• Be eye level when reading meniscus line to avoid parallax error

• Use small drops of indicator

• Use white tile paper behind the burette when reading burette value