Titrations practical questions

Why is it important to rinse the equipment with distilled water and not normal water?

To ensure ions from tap water dont affect the titre, by changing the moles and hence the concentration

What should you rinse the pipette with and why?

With the known solution and not water, as acid/ alkali would be diluted

What is a source of error in using the burette?

Not filling the jet space and leaving it full of air, as the titre will be larger than expected as it would seem like you added more of the solution in the burette than you actually did

Why is the funnel removed after filling the burette?

Small drops of liquid may fall from funnel into burette so the initial/ end volumes will differ, and it will look like you have added less acid/ alkali than you actually did

Suggest why, during the titration, the inside of the conical flask is rinsed with distilled water and how this improves the accuracy of the titre

In order to wash the sides to ensure all reagents are able to react together/ so it is washed in to react with the acid/ alkali

Why does adding this extra water not affect the volume of solution required in the titration

Adding water doesn’t affect number of moles of solution

Why is a conical flask used in preference to a beaker?

A conical flask allows you to swirl without contents spilling/ splashing out

how do you calculate % uncertainty?

uncertainty (given) / measurement made with apparatus x 100

How can you decrease apparatus uncertainty?

• use equipment with finer scale divisions, meaning the uncertainty will be lower

how would you work out the uncertainty for a piece of equipment you've used twice?

multiply the uncertainty by 2 (as you've used it twice) and carry on as normal

explain, using the same apparatus, how you can reduce the percentage uncertainty in using the burette.

you can decrease the concentration of the solution in the burette which would mean you'd have to use more, which would make the calculated uncertainty smaller which reduces error, as you are dividing by a bigger number

Suggest a safety precaution for filling the burette

Fill at eye level

Suggest a safety precaution for dissolving a toxic solid in water

wear gloves

What colour change is seen at the end point of titration

colourless to pink

practical steps needed before recording initial burette reading

remove funnel and remove air from jet space