PAG 02 - Acid-base Titration Flashcards
(20 cards)
What apparatus is used in a titration to accurately measure volumes
Burette to measure vol of solution added
Pipette + Pipette filler to measure specific vol of solution into conical flask
Describe weighing-by-difference method
- Add roughly the desired mass of a substance to a weighing bottle and weigh
- Transfer the substance to a beaker / conical flask
- Reweigh the weighing bottle
- The difference between the masses is the mass of solid
Describe how to carry out an acid-base titration
- Use a pipette to add 25 cm’ of acid to a conical flask. Add a few drops of indicator.
- Pour alkali into the burette. Record the initial burette volume.
- Complete a trial titre. The conical flask should be swirled constantly above a white tile.
Stop adding the alkali as soon as the end point is reached. Record the final burette volume. - Repeat the titration until two concordant results are obtained. Add alkali drop by drop near the end point.
(25cm’ of alkali may initially be put into the conical flask if the burette is filled with acid)
When transferring a solution from 1 beaker to another, how can you ensure as much of dissolved substance has been transferred as possible
Use distilled water to wash any leftover solution from old apparatus into new beaker
Hoe do you accurately fill a volumetric flask to graduated mark
Fill so bottom of meniscus rests on graduated mark
Meniscus is curve of liquid
What is a standard solution
Solution of known conc
Describe how to make standard solution of NaHCO3
- Weigh out a specified amount of NaHCO3
- Add a small volume of distilled water to the beaker containing the NaHCO3 to dissolve it
- Use a funnel to add the solution to a 250cm3 volumetric flask
- Rinse the beaker with distilled water and add the washings to the flask
- Make the flask up to the graduation mark with distilled water
- Stopper and shake the flask
Suggest 2 indicators that could be used in an acid-base titration
Phenolphthalein
Methyl orange
State colour of phenolphthalein in:
A) acidic conditions
B) basic conditions
A) colourless
B) pink
State colour of methyl orange in:
A) acidic conditions
B) basic conditions
A) red
B) yellow
(Orange at end point of titration)
What are concordant results in a titration
Titres that are within 0.1cm^3 of each other
What degree of precision should burette readings be recorded to
To nearest 0.05cm^3
Which results are used when calculating a mean titre
2 concordant results (within 1.10cm^3 of each other)
When completing a titration, what piece of apparatus is used to make colour change easier to observe
White tile
This is placed underneath conical flask
What 3 things are required to take an accurate burette reading
- Read from bottom of meniscus
- Allow any liquid on walls of burette to settle before taking a reading
- Ensure there are no air bubbles
What is end point of titration
1st point at which indicator changes colour (permanently)
Why is conical flask swirled during a titration
To ensure all reactants are combined so that reaction is complete
Why’s it better to have a titre vol of 25cm^3 than 10cm^3
Larger titre volume = smaller % error
What equation links no. Of mol and conc
n = c X v
If you know vol of acid required to neutralise an alkali, how could you calculate conc of acid, given alkali conc and vol
- Calculate the number of moles of the alkali using the known volume and concentration (n = C x V)
- Use chemical equation to work out the ratio of acid and alkali that react and hence work out how many mole of acid have reacted
- Divide the moles of acid by the volume used in neutralisation
