PAG 02- Acid Base Titration Flashcards
What apparatus is used in a titration to accurately measure volumes?
- Burette to measure volume of solution added
- Pipette and pipette filler to measure specific volume of solution into the conical flask
Describe the ‘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 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 25cm^3 of acid to a conical flask. Add a few drops of indicator.
- Pour alkali into a burette. Record initial burette volume.
- Complete a trial titration. The conical flask should be swirled constantly above a white tile. Stop adding alkali as soon as end point is reached. Record the final burette volume
- Repeat titration until two concordant results are obtained. Add alkali drop by drop at the end point
When transferring a solution from one beaker to another, how can you ensure as much of the dissolved substance has been transferred as possible?
Use distilled water to wash any leftover solution from old apparatus into the new beaker
How do you accurately fill a volumetric flask to the graduated mark?
Fill so the bottom of the meniscus rests on the graduated mark.
The meniscus is the curve of the liquid
What is a standard solution?
A solution of known concentration
Describe how to make a 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 250cm^3 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-bade titration
- Phenolphthalein
- Methyl orange
State the colour of phenolphthalein in:
a) acidic conditions
b) basic conditions
a) colourless
b) pink
State the 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 the nearest 0.05cm^3
Which results are used when calculating a mean titre?
2 concordant results (within 0.05cm^3 of each other)
When completing a titration, what piece of apparatus is used to make the colour change easier to observe?
A white tile.
This is placed underneath the 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 the end ooint of a titration?
The first point at which the indicator colour changes (permanently)
Why is the conical flask swirled during a titration?
To ensure all the reactants are combined so that the reaction is complete
Why is it better to have a titre volume of 25cm^3 than 10cm^3?
The larger the titre volume, the smaller the percentage error
What equation links number of moles and concentration?
moles= concentration x volume
If you know volume of acid required to neutralise an alkali, how could you calculate the concentration of the acid, given the alkali concentration and volume?
- Calculate number of moles of alkali using known volume and concentration
- Use chemical equation to calculate ratio of acid and alkali that react and hence work out how many moles of acid have reacted
- Divide the moles of acid by the volume used in neutralisation
