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6. A TITRIMETRIC DETERMINATION OF HYDROGEN
CARBONATE CONCENTRATION IN A WATER SAMPLE
6.1 Objective
Use a miniaturised and simplified acidimetric
titration to determine the concentration
of hydrogen carbonate in a water sample.
Use a syringe instead of a burette, and
use a Coulter-counter container as a replacement
for an Erlenmeyer flask.
6.2 Background
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Write the reaction on which the titration is based.
6.3 Equipment and reagents
- A device for miniaturized titration.
- A standard solution of hydrochloric
acid, concentration 0.1 mol/L.
- A solution of bromochresol green
(Phenol, 4,4'-(3H-1,2-benzoxathiol-3-ylidene)
bis[2,6-dibromo-3-methyl-, S,S-dioxide)
indicator.
Hazards
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Hydrochloric acid
is corrosive. Avoid inhalation
or contact with skin.
R: 34-37, S: 26-45
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6.4 Procedure
- Fill the syringe with the standard
solution of HCl.
- Fill the Coulter-counter container
with the water sample up to the first
mark (V=10 ml).
- Add a drop of the bromocresol green
indicator solution to the sample.
- Titrate the examined solution until
its colour changes to pale green. Be
careful, the solution must not turn
yellowish-green.
- Record the volume of HCl solution
consumed during the titration from the
syringe.
Note. &
The procedure can be made easier by
first estimating the volume of HCl standard
solution that is needed to reach the
end-point of the titration. Start with a
preliminary titration in which the HCl solution
is added in 0.05-ml increments.
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Calculation of the result:
Calculate the amount and the mass concentration
of hydrogen carbonate in the water sample.
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cHCO3_
=
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cHCl
. VHCl
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g HCO3_
= cHCO3_ . MHCO3_
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Vsample
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MHCO3_ = 61.00 g/mol
Write both results in the table “Results – Major components”,
under the serial number of the sample.
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