PAG 2- Acid-base titrations Flashcards
1
Q
Making a standard solution method
A
- Weigh required mass of solid in a weighing boat on a 2d.p mass balance (for resolution).
- Transfer to a 250cm^3 beaker.
- Add a small volume of distilled water to the beaker and stir using a glass rod until the solid completely dissolves.
- Transfer the solution to a 250cm^3 volumetric flask using a funnel.
-Rinse the beaker and the glass rod with distilled water, adding washings to volumetric flask. - Fill up to the graduated line using distilled water, ensure bottom of meniscus sits on line.
- Use dropping Pipette for last few drops.
- Place stopper and invert several times to mix the solution.
2
Q
How could mass be measured more accurately?
A
- Measure on a 2/3 d.p mass balance of weighing boat with solid in it.
- Empty solid into flask.
- Reweigh the empty weighing boat and then subtract original mass from final mass to find the exact mass actually added.
3
Q
Method for finding conc of HCl by titration
A
- Rinse the volumetric pipette with the substance to be added to it.
- Pipette 25cm^3 of solution A into a conical flask, fill to graduation line, bottom of meniscus should sit on it.
- Touch surface of solution with pipette, to ensure correct amount is added, and to calibrate.
- Rinse the burette with the substance to be added to it, prevents dilution by any existing water or left over substances, would cause concentration of substance to be lowered and a larger titre to be delivered than needed.
- Don’t leave the funnel in the burette, because small drops may fall in during the titration, which would lead to a lower titre volume.
- Make sure air bubbles are removed, to prevent larger reading than expected of titre.
- Add a few drops of indicator to the conical flask, not too many.
- Add solution from burette into conics, flask whilst swirling the mixture and *add drop- wise at the end point** (where colour change occurs).
- Note burette reading and then repeat titration until at least 2 concordant titres (within 0.10cm^3 of each other) are obtained (removes anomalies), read from bottom meniscus.
4
Q
Indicators and colour changes
A
-Phenolphthalein- pink (alkali), colourless (acid)
-Methyl orange- yellow (alkali), red (acid)
