Core practical - Acid-alkali titration Flashcards
Method: (5)
1- Use a pipette to add 25 cm3 of dilute sodium hydroxide solution to a clean conical flask.
2- Add a few drops of phenolphthalein indicator and put the conical flask on a white tile.
3- Fill the burette with dilute hydrochloric acid and note the starting volume.
4- Slowly add the acid from the burette to the conical flask, swirling to mix. Stop adding the acid when the end-point is reached (when the colour first permanently changes from pink to colourless). Note the final volume reading.
5- Repeat steps 1 to 5 until you get concordant titres (see step 1 in the Analysis).
how could the analysis of the titres be conducted? (2)
use two concordant titres that are within 0.20 cm3 (or sometimes 0.10 cm3) of each other
-calculate the mean titre
Describe three steps needed to obtain accurate results.
-Make sure the burette is vertical,
-take the readings from the bottom of the meniscus.
-Near to the end-point, rinse the inside of the flask with distilled water & add the acid drop by drop
Explain why a pipette is used to measure the acid, rather than a measuring cylinder.
The pipette allows the same volume of acid to be added each time, helping to make the results repeatable.
the harms caused by and the precautions needed for: Dilute sodium hydroxide solution
Causes skin irritation and serious eye irritation
Wear gloves and eye protection, and use a pipette filler
the harms caused by and the precautions needed for: Spilling hydrochloric acid while filling the burette
Causes eye irritation
Fill the burette slowly below eye level, using a funnel
Concentrations using moles equation:
concentration (in mol/ dm^3) = amount of solute in mol/ volume in dm^3
what can the units of concentration be displayed as?
mol dm3 or M
what is needed to convert between mol dm-3 and g dm-3:
the relative formula mass
how could you convert between mol dm-3 to g dm-3? (2)
to convert from mol dm-3 to g dm-3, multiply by the Mr
to convert from g dm-3 to mol dm-3, divide by the Mr
