QUANTITATIVE DETERMINATION OF SODA ASH COMPOSITION BY DOUBLE INDICATOR TITRATION

J. OLIVEROS1

1INSTITUTE OF BIOLOGY, COLLEGE OF SCIENCEUNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY 1101, PHILIPPINESDATE SUBMITTED: 4 MARCH 2015DATE PERFORMED: 27 FEBRUARY 2015

DISCUSSION

1.Why the distilled water to be used in this experiment need to be boiled?- It was boiled to get rid of the carbon dioxide that was originally found in the water. This carbon dioxide may react/provide erroneous results if left within the system of titration. This is because carbon dioxide, dissolved in water, may form carbonic acid. This compound might react with the base components of soda ash.

2. Why is a mixture of NaOH and NaHCO3 incompatible?- OH- from NaOH and HCO3

- from NaHCO3 would react with each other : OH- + HCO3- >> H2O + CO32-

This reaction would cause a decrease on both OH- and HCO3- concentration and production of

carbonate ions which can alter the volumes of the HCLstandard.

3. Why is there a need to boil the solution before reaching the methyl orange endpoint? - There is a need to boil the solution for the reaction of the titration to obtain the Vmo that aims to neutralize the HCO3- leads to the formation of carbonic acid which can alter the color of the solution with the methyl orange indicator, and in order to get rid of the carbonic acid, it needs to be boiled.

4. What are the basic components? - The data obtained support the assumption that the soda ash components are NaHCO3 and Na2CO3.

The two volumes Vmo and V ph are theoretically equal/similar in the titration of Na2CO3. The reason for this is because the V ph of HCl that neutralizes the carbonate ion into a bicarbonate ion, and the Vmo is used to neutralized the same number of moles of the bicarbonate ion. In the experiment, the V mo obtained is greaterthan V ph, which means there are more bicarbonate ions in the solution than carbonate ion. This suggests thats NaHCO3, a base that can supply bicarbonate ions, is also present in the soda ash

5. Possible sources of errors?- Errors may be found and acquired by uncertainties in the measurements of the components in the experiment. Uncertainties in measurements of the solutions can cause an increase or decrease in the needed volume of the solutions and can change the results in the analysis of soda ash. Errors in reading the volume of the titrant used can cause errors in the calculated HCl concentrations. Another source of error is the determination of the endpoint of the titration since it was based on the color change, because of this, inevitable human error can be at play, the observers could have assumed that the endpoint was reached earlier than the exact time and some could have seen an erroneous pink color. This can increase the molarity of the HCl. The dissolved carbon dioxide can also be a source of error because it can interfere with the methyl orange color thus increasing the molarity of the titrant.