The action of heat on a solid hydrogencarbonate

Variables

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Safety and Precautions

1. Read burette readings at meniscus level
2. Towards the end, add the solution drop by drop and swirl to avoid errors
3. Take away the funnel from the top of the burette when the HCl solution is poured
4. All apparatus rinsed with deionised water and their respective solutions
5. Take care of the pipette fillers by not letting the solution overshoot into the fillers
6. Put a plain paper underneath the volumetric flask to easily note the colour change
7. Measure accurately exactly the value given for the amount of substance and no more or less

Apparatus

        Instruments:

• 250cm3 conical flask
• 250cm3 volumetric flask
• 50.0cm3 burette × 2
• crucible
• mass balance
• funnel
• beakers
• tripod stand
• Bunsen burner
• matches

        Chemicals:

• solid A
• methyl orange indicator
• distilled water
• 0.1M hydrochloric acid
• 0.1M sodium hydroxide
• deionised water

Diagram

Procedure

        Experiment 1

• Note down the mass of an empty crucible
• Weight accurately about 8 g of solid A into the crucible
• Reweigh the total mass
• Heat the solid A over a Bunsen burner for 5 minutes at maximum heat
• Allow the residue B to cool down
• Measure the new mass of residue B
• Further heat the residue for 3 more minutes, allow it to cool down and measure the mass again
• Repeat this until there is no further mass change

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        Experiment 2

• Take about 4.25 g of solid A and place it into a 250 cm3 volumetric flask
• Fill up the flask up to the 250 cm3 mark with distilled water
• Shake the flask thoroughly until all of the solid A has been mixed
• To test if the hydrochloric acid is indeed 0.1M, a standardisation experiment must be carried out:

• Fill up a burette with hydrochloric acid
• Take about 25 cm3 of 0.1M sodium hydroxide in a beaker
• Add a few drops of methyl orange indicator to the beaker
• Titrate the solution with the HCl and record the HCl reading

• Titrate 25.0 cm3 portions of this solution with 0.1M hydrochloric acid
• Repeat the titration experiment three times and note down the HCl reading

        Experiment 3

• Place about 2.5 g of the solid residue B in a volumetric flask
• Fill up the flask up to the 250 cm3 mark with distilled water
• Shake the flask thoroughly until all of the solid A has been mixed
• Titrate 25.0 cm3 portions of this solution with 0.1M hydrochloric acid
• Repeat the titration experiment three times and note down the HCl reading

Data Collection

        Experiment 1

        Experiment 2

        Standardisation experiment

        Experiment 3

        Mass of solid B = 2.50 g

Data Processing and Presentation

The cation of hydrogencarbonate and carbonate in the above experiments is unknown. Let’s assume that the cation is sodium.

Reaction in Experiment 1

Ratio of moles of NaHCO3 : Na2CO3 = 2 : 1

Mass of hydrogencarbonate = 8.00 g

RMM of solid A (hydrogencarbonate) = 84.0 g

Mass of residue carbonate = (38.88 – 34.03) = 4.85 g

RMM of solid B (carbonate) = 106 g

Reaction in Experiment 2

Ratio of moles of NaHCO3 : HCl = 1 : 1

Mass of NaHCO3 = 4.25 g

RMM of NaHCO3 = 84.0 g

Volume (average titre) of HCl = 49.33 cm3 = 0.04933 dm3

Concentration of HCl = 0.1 mol dm-3

Reaction in Experiment 3

Ratio of moles of Na2CO3 : HCl = 1 : 2

Mass of Na2CO3 = 2.50 g

RMM of Na2CO3 =106 g

Volume (average titre) of HCl = 43.97 cm3 = 0.04397 dm3

Concentration of HCl = 0.1 mol dm-3

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Error in measurement

Conclusion and Evaluation

The percentage error for the volumetric analysis experiment is 4.5% while the gravimetric experiment gave 6% errors, which are both fairly low. However, as volumetric analysis gave a smaller error than gravimetric, the results are more reliable than the one performed using gravimetric analysis, proving my hypothesis correct.

The error might have been caused due to a number of reasons. For example, in the gravimetric analysis, the main cause of error could be heating the solid A for before it had stopped showed signs of mass change. It could also be that the mass was not measured properly on the mass balance. There is also a risk of slight spillage.

In the volumetric analysis, the error could have been caused mostly by human error.  The human eye could not have been able to record the colour change early enough to close the tap of the burette. The volumetric analysis still gave a more accurate result mainly due to the accuracy of the equipment such as burette.

To reduce the error in the whole experiment, it could be performed a few times and an average could be taken. One could also trying using more accurate equipment than equipment such as mass balance.

For further experiments, one could experiment with different types of hydrogencarbonate, or could also try using different types of analysis. One more type of analysis known is colorimetric analysis.

References

• “Chemistry Study Guide”, Thomson Learning, [Online] Available from “” [Accessed 25 Oct 2005]

• Henry P. Talbot, “An Introductory Course of Quantitative Chemical Analysis With Explanatory Notes”, [Online] Available from “” [Accessed 25 Oct 2005]

• “School Science Lessons”, University of Queensland, Brisbane, Australia, [Online] Available from “” [Accessed 24 Oct 2005]

• “Gravimetric analysis - encyclopedia article about Gravimetric analysis”, [Online] Available from “” [Accessed 25 Oct 2005]

• “Dictionary Definition: Volumetric Analysis”, [Online] Available from “” [Accessed 25 Oct 2005]

• Tim DeLaney, “Gravimetric vs. Analysis?” [Online] Available from “” [Accessed 25 Oct 2005]

• E N Ramsden, “A-Level Chemistry”

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