This document provides instructions for estimating the amounts of sodium carbonate and sodium bicarbonate present in a mixture. The experiment involves titrating a sample of the mixture against a standardized hydrochloric acid solution using the pH indicators phenolphthalein and methyl orange to determine the endpoints of the reactions of carbonate and bicarbonate ions with hydrogen ions. Phenolphthalein can be used to detect only the reaction of carbonate ions, while methyl orange is needed to detect the complete neutralization of both carbonate and bicarbonate ions.

1. SHREE MALLIKARJUN COLLEGE
CLASS:FYBSC
SAFETY: Refer to MSDS of hydrochloric acid, sodium bicarbonate, sodium carbonate,
phenolphthalein and methyl orange
-Dr. Mithil S.Fal Desai
Aim: Estimation of sodium carbonate and sodium hydrogen carbonate present in a mixture.
Chemicals: Hydrochloric acid, sodium carbonate, sodium bicarbonate, methyl orange and
phenolphthalein.
Apparatus: Standard volumetric flask, pipette, burette, conical flask, beakers,funnel and glass rod.
Theory: The completion of Reaction-2 can be analyzed using phenolphthalein or methyl orange indicator.
However complete neutralization of bicarbonate (Reaction-2) cannot be studied using phenolphthalein
indicator. The mixture of carbonates and bicarbonate as solution will be pink in colour once the available
carbonate forms bicarbonate ( around pH )8. Thus, Reaction-2 could be effectively studied using methyl
red indicator only.
CO3
2-
(aq) + H+
(aq)  HCO3
-
(aq) (Reaction-1) Methyl red and phenolphthalein
HCO3
-
(aq) + H+
(aq)  H2CO3 (aq) H2O (l) + CO2 (g) (Reaction-2) Methyl red
The use of pH sensitive indicators such as phenolphthalein [colourless pH(8.0-9.6) pink] and methyl
orange [red pH(3.1- 4.4) yellow] can differentiate these chemical species by neutralization with dilute
mineral acids.
Procedure:I) Standardisation of 0.1 (appx.) HCl (Refer-2)
II) Estimation of bicarbonate and carbonate in mixture.
1) Pipette out 10 mL of mixture in a conical flask add 2 drops of methyl orange indicator.
2) Titrate against standardized 0.1N HCl (appx.) solution and repeat the titration for constant
readings.
3) Similarly, titrate the 10 mL of mixture against standardized 0.1N HCl using phenolphthalein
indicator
4) Repeat the titration until a constant reading is observed.
Further reading (available in library)
1) Experiments in Applied Chemistry, S. Rattan,S. K Kataria and Sons.
2) Vogel’s textbook of quantitative chemical analysis, J. Mendham, R. C. Denney, J. D. Barns, M.
Thomas, B. Sivasankar, Pearson India Education, 6th
Edition.
Questions
1) Which amongst the following is/are the primary standards? Why?
HCl, Na2CO3,NaHCO3
2) What is the equivalent weight of Na2CO3 and NaHCO3 according to reaction 1 and 2?
3) Why an indicator is required in the experiment?