titration Flashcards
Volumetric analysis
a quantitative analysis in
which the concentration of a substance is
determined by measuring the volume of one
solution required to react with a given known
volume of another solution.
what should be carried out to do volumetric analysis
titration
In titration, the concentration of one solution should be accurately known, what is it called
standard solution
how can a standard solution be prepared
dilution
dissolving a known mass of a substance into a known volume of deionized water.
dilution
● Standard solution with a desired concentration can be prepared from a more
concentrated stock solution.
● Certain volume of the stock solution is mixed with deionized water in a volumetric
flask.
● Adding water to a concentrated solution:
○ changes the concentration of the solution
○ does not change the number of moles of solute present
No. of moles of solute before dilution = No. of moles of solute after dilution
C1 x V1= C2 x V2
○ C1 and C2
- concentrations (in mol dm-3)
○ V1 and V2
- volumes of solution (in dm3
Preparing standard solution by dilution
use a pipette to obtain 25.0cm^3 of 2.0 mol dm^-3 H2SO4
transfer the acid to a 100cm3 volumetric flask containing a little distilled water. Shake to mix the solution. add more distilled water to the flask, with constant swirling
water is added dropwise to bring the solution to the calibration mark. stopper the flask and shake well to ensure thorough mixing
how can The volume of stock solution
required must be measured out
accurately
● Use a pipette to measure
out exactly 25.0 cm3
of stock solution.
● Use a burette to measure
out any other volumes that
are less than 50.0 cm3
.
Preparing a standard solution by weighing method
- The mass of solute needed is calculated and weighed.
- The solute is dissolved in some distilled water in a beaker.
- The solution is transferred into a volumetric flask.
- More distilled water is added to top up to the required volume.
- The flask is stoppered and inverted a few times.
Titration
Titration is used to determine the concentration of an analyte (substance to be
analysed).
A reagent
A reagent, termed the titrant, is prepared as a standard solution of known
concentration and volume.
● The titrant is commonly delivered by burette into a known volume of the solution
with the analyte (called aliquot) in a conical flask.
○ Note that the analyte can sometimes be delivered by burette.
how long is the titrant added
● The titrant is added to the
solution of analyte until it has
reacted in the exact quantity
stoichiometrically with the
analyte - the equivalence point.
● However, it is difficult to detect
the equivalence point practically.
End-point of titration
● Instead, the end-point of the titration will be detected.
● It is achieved when an additional drop of titrant is added to the solution in the flask.
● This point is marked by an indicator,
which is added to the solution in the
conical flask before the start of titration.
● If the point is reached, a colour change
of the indicator will be observed.
Experimental set-up of titration
● Burette - transfers varied known
volume of titrant to the conical flask
● Conical flask - holds the aliquot
(transferred by a volumetric pipette)
with several drops of indicator
added.
● White tile - provides a white
background for better observation of
colour change at the end-point.
indicator choice (strong acid + strong base)
HCl + NaOH
methyl orange or phenolphthalein
indicator choice (strong acid + weak base)
HCl + NH3
methyl orange
