Sichuan University
Question
Asked 10 May 2014
How can I be sure regarding the endpoint of Na2CO3 vs HCl titration?
0.1 N concentration solution of both was taken, with HCl as titrant abd HPh as indicator. After reaching the endpoint of colourless condition, the colour reappears after continous shaking for 5 mins. even sometimes after 15 mins. How to be sure of that this much time is enough, for shaking to confirm completion of titration?
Most recent answer
Hello,
Determining the endpoint of a titration between sodium carbonate (Na2CO3) and hydrochloric acid (HCl) with accuracy is critical for obtaining precise results. Sodium carbonate reacts with hydrochloric acid in a two-step neutralization reaction, and identifying the endpoint requires careful consideration of the reaction mechanism and the appropriate indicators. Here are the steps and considerations to ensure accuracy:
- Understanding the Reaction: The reaction between Na2CO3 and HCl is a two-step neutralization process. Initially, Na2CO3 reacts with HCl to form sodium bicarbonate (NaHCO3) and then NaHCO3 further reacts with HCl to form sodium chloride (NaCl). Each mole of Na2CO3 reacts with two moles of HCl.
- Choice of Indicator: The selection of the right indicator is crucial. For this titration, methyl orange is a suitable choice. Methyl orange changes color at a pH of 3.1 to 4.4, which aligns well with the pH change expected at the endpoint of the reaction between Na2CO3 and HCl.
- Preparing the Solution: Dissolve a known quantity of Na2CO3 in a measured volume of distilled water. Ensure complete dissolution of the salt for an accurate starting concentration.
- Performing the Titration:Fill a burette with standardized HCl solution. Add the Na2CO3 solution to a conical flask and add a few drops of methyl orange indicator. Slowly add the HCl from the burette to the Na2CO3 solution, swirling the conical flask continuously for uniform mixing. Observe the color change of the solution. The endpoint is reached when the color changes from yellow to pink and remains so even after thorough mixing.
- Monitoring pH Changes: For more precision, a pH meter can be used alongside the indicator. This allows for the monitoring of pH changes during the titration, providing a more accurate determination of the endpoint.
- Repeat for Consistency: Conduct multiple titrations for consistency and to ensure repeatability of results. The average of consistent readings should be taken for calculation.
- Calculation: Once the endpoint is accurately determined, use the volume of HCl used to calculate the concentration of the Na2CO3 solution, considering the stoichiometry of the reaction.
- Consideration of Carbonate to Bicarbonate Transition: Be aware that the first reaction (carbonate to bicarbonate) is relatively rapid, while the second reaction (bicarbonate to chloride) is slower. The accurate endpoint is for the second reaction.
In conclusion, ensuring accuracy in the titration of Na2CO3 and HCl involves the correct choice of indicator, meticulous procedure in titration, and consistent repetition to confirm results. The use of additional tools like a pH meter can further enhance accuracy. Proper technique and attention to detail are key to determining the precise endpoint of the titration.
Perhaps this protocol list can give us more information to help solve the problem.
All Answers (6)
Institute for Technological Research
titration of carbonates and bicarbonates is an intricate problem. carbon dioxide from the atmosphere can interfere with the titration. I suggest soaking the tip of the burette the solution.

I would suggest to use Carbondioxide free water for sodium carbonate titrations. CO2 free water can be produced by boiling the normal purified water and then covering it with a foil s oas to avoid intact with air, cooling it to room temperature and then doing the titrations.
Also some methods also suggest to warm the conical flask on colour change and indicate the colour should persists even after the solutions are heated. It is only then the titration has reached its end point.
1 Recommendation

Otherwise determinig the eqivalence point potentiometrically is the best suitable option.
1 Recommendation
Krause Analytical
No question; Rashmi's answer is the correct one. Use potentiometry. The color indicator is adequate for rough work, but if you want really precise work you need to use potentiometry.
Bangabandhu Sheikh Mujibur Rahman Science and Technology University
in case of titration, 0.1 N sodium carbonate solution the required hcl concentration is concentrated or 0.1 N solution used.
Sichuan University
Hello,
Determining the endpoint of a titration between sodium carbonate (Na2CO3) and hydrochloric acid (HCl) with accuracy is critical for obtaining precise results. Sodium carbonate reacts with hydrochloric acid in a two-step neutralization reaction, and identifying the endpoint requires careful consideration of the reaction mechanism and the appropriate indicators. Here are the steps and considerations to ensure accuracy:
- Understanding the Reaction: The reaction between Na2CO3 and HCl is a two-step neutralization process. Initially, Na2CO3 reacts with HCl to form sodium bicarbonate (NaHCO3) and then NaHCO3 further reacts with HCl to form sodium chloride (NaCl). Each mole of Na2CO3 reacts with two moles of HCl.
- Choice of Indicator: The selection of the right indicator is crucial. For this titration, methyl orange is a suitable choice. Methyl orange changes color at a pH of 3.1 to 4.4, which aligns well with the pH change expected at the endpoint of the reaction between Na2CO3 and HCl.
- Preparing the Solution: Dissolve a known quantity of Na2CO3 in a measured volume of distilled water. Ensure complete dissolution of the salt for an accurate starting concentration.
- Performing the Titration:Fill a burette with standardized HCl solution. Add the Na2CO3 solution to a conical flask and add a few drops of methyl orange indicator. Slowly add the HCl from the burette to the Na2CO3 solution, swirling the conical flask continuously for uniform mixing. Observe the color change of the solution. The endpoint is reached when the color changes from yellow to pink and remains so even after thorough mixing.
- Monitoring pH Changes: For more precision, a pH meter can be used alongside the indicator. This allows for the monitoring of pH changes during the titration, providing a more accurate determination of the endpoint.
- Repeat for Consistency: Conduct multiple titrations for consistency and to ensure repeatability of results. The average of consistent readings should be taken for calculation.
- Calculation: Once the endpoint is accurately determined, use the volume of HCl used to calculate the concentration of the Na2CO3 solution, considering the stoichiometry of the reaction.
- Consideration of Carbonate to Bicarbonate Transition: Be aware that the first reaction (carbonate to bicarbonate) is relatively rapid, while the second reaction (bicarbonate to chloride) is slower. The accurate endpoint is for the second reaction.
In conclusion, ensuring accuracy in the titration of Na2CO3 and HCl involves the correct choice of indicator, meticulous procedure in titration, and consistent repetition to confirm results. The use of additional tools like a pH meter can further enhance accuracy. Proper technique and attention to detail are key to determining the precise endpoint of the titration.
Perhaps this protocol list can give us more information to help solve the problem.
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