RP1 - Making a Volumetric Solution and Acid-Base Titration Flashcards
How to accurately measure the mass of a solid
Weigh the sample bottle containing the required mass of solid on a 2dp balance
Transfer to a beaker, washing the bottle and adding to the beaker.
Reweigh the empty sample bottle
Record the difference in mass
How to make a solution using an already measured mass of solid.
Add the solid to a beaker and add distilled water and use a glass rod to dissolve the solid.
Transfer the solution into a 250cm^3 graduated flask via a funnel.
Rinse beaker and funnel and add washings to the volumetric flask.
Make up to the 250cm^3 mark with distilled water
Shake the flask.
Why do we have to shake the volumetric flask when making solution
To ensure a uniform concentration
Why can we not heat or put hot solutions in the volumetric flask
The heat causes the flask to expand and the volume would then be incorrect
Describe how we can dilute a solution
Pipette 25cm^3 of the original solution into a 250cm^3 volumetric flask.
Make up to the 250cm^3 mark with distilled water, using a dropping pipette for last few drops
Shake/invert the flask several time times to ensure uniform solution
Concordant results
Readings within 0.1 of each other
Why is a conical flask used instead of a beaker in titrations
Easier to swirl the mixture in a conical flask without spilling the contents
What should you do to the burette before using
It should be rinsed out with substance that will be put in it.
If not rinsed out the acid/alkali added may be diluted by residual water or may react with previous substances.
This would decreases the concentration of the substance and so you would get a larger titre.
Why do we have to remove the funnel from the burette
Small drops of liquid may fall from the funnel during titration leading to false burette reading and gives a lower titre volume
What must we do to the jet space in the burette before using
Ensure it is filled with the solution and air bubbles are removed.
How must you read the burette
From the bottom of the meniscus
How much indicator should you add and why
A few drops as indicators are weak acids so if too much is added they will affect the titration results
Which reactions are phenolphthalein used in
When strong alkalis are used
Colour change when acid is added from burette to the alkali (phenolphthalein)
Pink in alkali to colourless
Which titration reactions are methyl orange used in
When strong acids are used
Colour change for methyl orange
Red in acid
Yellow in alkali
Orange at end point
Why is a white tile used
To help observe the colour change
How should you add solution from burette
Whilst swirling the mixture and adding drop wise at end point
Why might distilled water be added to the conical flask during a titration
To wash the sides of the flask so all the acid on the side is wash into the reaction mixture to react with the alkali.
Why does distilled water being added into the conical flaks not affect the titration readings
Water does not react with the reagents or change the moles of acid added.
Why are titrations repeated
To spot anomalous results and so they can be discounted
To find concordant results
To calculate an average
Colour of MnO4 -
Purple
Colour change if manganate is in the burette
Colourless to purple
% uncertainty =
Uncertainty / Measurement x 100
