PAG 02 — Acid Base Titration Flashcards
What apparatus is used in a titration to accurately measure volumes?
- Burette to measure the volume of solution added
- Pipette and pipette filler to measure a 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 the weighing bottle
- The difference between the masses is the mass of the 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 the burette. Record the initial burette volume.
- Complete a trial titre. The conical flask should be swirled constantly above a white tile. Stop adding as soon as end point is reached. Record final burette volume.
- Repeat until you have two concordant results. Add alkali drop by drop near the endpoint.
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 the old apparatus into the new beaker.
How do you accurately fill a volumetric flask to the graduated mark?
Fill so bottom of meniscus rest on the graduated mark.
What is a standard solution?
A solution of a 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-base titration.
- Phenolphathalein
- 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
Which results are used when calculating a mean titre?
2 concordant results
What 3 things are required to take an accurate burette reading?
- Read from the bottom of the meniscus
- Allow any liquid on the walls of the burette to settle before taking a reading
- Ensure there are no air bubbles
What is the end point of a titration?
The first point at which the indicator changes colour (permanently)
Why is it better to have a titre volume of 25cm^3 that 10^3?
The larger the titre volume, the smaller the percentage error
What equation links no. Moles and concentration?
n = C x V
