Acid-Base Titrations Flashcards
Based on the OCR specification.
What are titrations used for?
To find:
-The concentration of a solution
-Identification of unknown chemicals
-The purity of a chemical
What is a standard solution?
A prepared solution with a known concentration
What is used to prepare standard solutions?
A volumetric flask
What is the typical tolerance of an 100 cm^3 volumetric flask?
±0.20cm^3
What is the typical tolerance of a 250 cm^3 volumetric flask?
±0.30cm^3
How do you prepare a standard solution?
-Accurately measure the solid
-Dissolve the solid in a beaker with less water than the volumetric flask and pour it in.
-Continue adding water to the solution until it exactly reaches the line of the volumetric flask
-Invert the flask to ensure everything is evenly distributed/dissolved
How do you make sure that the volumetric flask has been filled accurately?
Make sure the bottom of the meniscus touches the line and view the meniscus from eye-level.
What should the last decimal place always be in a burette reading?
0 or 5
Is the unknown solution or the standard solution in the burette?
The unknown solution.
What should the standard solution be in?
Conical flask
How many drops of indicator should usually be added to a standard solution?
2-3 drops
Why are rough titres carried out?
To find an approximate amount of unknown solution to add for the standard solution to change colour.
Should you generally wait until the most extreme colour of solution is achieved until stopping the titration?
No, you would have added too much solution.
What are concordant results?
Results that are in 0.1 cm^3 of each other
What results should you omit from mean titre calculations?
Rough titres and non-concordant titres.
What equation links moles, volume and concentration?
n = c x v/1000
How do you find concentration if you know the moles and the volume of a solution?
c = n x 1000/v
What are common indicators for titrations?
-Methyl Orange
-Phenolphthalein
Why isn’t universal indicator used in titrations?
Hard to determine the PH of a solution due to the differing ranges of colours
What colour does phenolphthalein change into when in acid?
Colourless
What colour does phenolphthalein change into when in a base/alkali?
Pink
What colour does methyl orange turn into when in acid?
Deep red
What colour does methyl orange turn into when in a base/alkali?
Yellow
