module 2 - acid-base titrations Flashcards
what’s a titration?
a technique used to accurately measure the volume of one solution that reacts exactly with another solution
what are 3 things can titrations be used for?
- finding concentration of a solution
- identification of unknown chemicals
- finding the purity of a substance
what’s a standard solution?
a solution of known concentration
what is used to make a standard solution?
a volumetric flask
what is a volumetric flask used for in titrations?
to make up a standard solution very accurately
why is using a volumetric flask good?
because they can measure volumes very precisely
what are the 1st 3 steps in preparing a standard solution?
- weigh solid accurately
- dissolve solid in a beaker using distilled water (less than what will be needed to fill the vol flask to the mark)
- transfer this solution to vol flask. (last traces of solution are rinsed into the vol flask with distilled water)
what next step is taken after rinsing and solution are first put into the volumetric flask?
- flask is filled to the graduation line by adding distilled water one drop at a time until the bottom of the meniscus lines up exactly with the mark
why is it important to be careful when filling up the volumetric flask completely?
- if too much water is added, the solution = too dilute and must be made again
how should you view the graduation mark and meniscus and why?
- at eye-level
- for accuracy
what’s the final step after the volumetric flask is completely filled?
- its slowly inverted several times, to mix the solution thoroughly and evenly
what happens if you dont invert the mixture?
- titration results are unlikely to be consistent
how can you see the solution mixing when yo invert the vol flask?
the more dense original solution moves through the solution
what is the effect on the titre with the error of filling the flask with water above the grad line?
the titre would be less as solution is more dilute
what is the effect on the titre when in error, the flask is not inverted?
- the solution used in the first titration would be more dilute than the solution used after.
- The first titre would need less solution
in an acid-base titration what is titrated against what?
a solution of an acid is titrated against a solution of a base using a pipette and a burette
how is a burette reading recorded?
to the nearest half division
what is each burette reading measured to? what does this mean?
to the nearest +/- 0.05cm^3
- the reading always has 2 dp
- last decimal place is always 0/5
what should you do when filling a burette to remove air bubbles?
run excess solution out through the tap
where would you put the acid and alkali in a titration to find the concentration of hydrogen ions in an acid solution
- put acid in burette
- put alkali in conical flask
what are the 1st 3 steps in doing an acid-base titration (before turning tap on)??
- add a measured volume of 1 solution (usually unknown one) to a conical flask using a pipette
- add the other solution (usually the standard solution) to the burette, and record the initial burette reading to nearest 0.05cm^3
- add a few drops of indicator to the conical flask solution!!
for a titration, what is the step after the indicator is put in?
- run burette solution into conical flask, swirling the con. flask throughout it to mix both.
- soon, the indicator changes colour at the end point of the titration
what does the end point do?
it’s used to indicate the volume of 1 solution that exactly reacts with the volume of the 2nd solution.
after the end point is reached in a titration what is the next step?
- record the final burette reading
