NALYSIS S QUANTITATIVE ANALYSI TITRATION
OF
SODA ASH
BY
DOUBLE-INDICATOR
S.A.P S.A.P.. S AAVEDRA M.C.Z. Z. PORTEZA3 AAVEDRA1, J . C . V ILLASIS2, J.T. LIM2 AND M.C. 1 N ATIONAL I NSTITUTE NSTITUTE OF P HYSICS HYSICS , C OLLEGE OLLEGE OF S CIENCE CIENCE 2 DEPARTMENT OF F OOD , C OLLEGE E CONOMICS OOD S CIENCE CIENCE AND N UTRITION UTRITION OLLEGE OF H OME OME E CONOMICS 3 DEPARTMENT OF M INING INING , M ETALLURGICAL ETALLURGICAL AND M ATERIALS E NGINEERING NGINEERING , C OLLEGE OLLEGE OF E NGINEERING NGINEERING U NIVERSITY , Q UEZON C ITY NIVERSITY OF THE P HILIPPINES HILIPPINES , D ILIMAN ITY , P HILIPPINES HILIPPINES DATE PERFORMED : JUNE 22, 2016 INSTRUCTOR ’S NAME: GARRERO, M.J. M.J.
1. Why Why is ther there e a need need to to boil boil the the dist distil ille led d watter in the wa the prepar eparat atiion of base ase solutions?
3. Why Why is is ther there e a need need to boil boil the the solu soluti tion on befo before re reach reachin ing g the the meth methyl yl orang orange e endpoint?
Boil Boiling ing disti distill lled ed wate waterr is esse essent ntia iall to remo remove ve diss dissol olve ved d carb carbon on diox dioxid ide e (CO (CO2) presen presentt in the solution solution.. Presenc Presence e of CO2 in water makes the solution slightly acidic. CO 2 solubility increases with pH, thus addition of base solution will cause a redox reaction to occur, occur, for forming ming a buffe bufferr soluti solution. on. This This will will affect the concentration of base solution and then then the accur accurac acy y of the determ determina inatio tion n of endpoint.
As wit with boilin iling g dis distil tilled wate water, r, the the solu solutio tion n is boil boiled ed befo before re reac reachin hing g meth methyl yl orange orange endpoin endpointt to remov remove e dissol dissolve ved d CO2. Non removal of CO 2 can cause buffer solution, affecting affecting reading reading of methy methyll orange orange endpoint. endpoint.
2. Why Why is the mixtu mixture re NaOH NaOH and NaHC NaHCO O3 incompatible? NaOH is a strong strong base in natu nature re while while NaHCO3, which acts as base in a reaction with HCl, can also act as a weak acid. A mixture of the the two comp compou ounds nds give: give: (1)
4. Discu Discuss ss the the basi basic c compo compone nents nts of the the unkn unknown own soda soda ash ash samp sample le base based d on the volume relationship at the phenol phenolph phtha thalei lein n and methyl methyl orange orange endpoints Titration is first done using the phenolphthalein indicator, noting that initial solution is basic. Net Volume 1 (V 1) indicates the volume needed to reach solution endpoint (change from fuchsia pink to colorless). Once reached, reached, a second indicator, indicator, methyl methyl orange, orange, was was used used to dete determ rmin ine e seco second nd solu soluti tion on endpoint. Net Volume 2 (V2) indicates volume needed needed to reach reach solution solution endpoint endpoint from V1.
This This will will then then react react in a neutra neutraliz lizati ation on reacti reaction. on. In general general,, NaOH NaOH and NaHCO NaHCO3 is incompatible.
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TABLE 1. Volume Relationship of the Possible Components of the Soda Ash Sample Component
Volume Relationship
Na2CO2 NaHCO3 NaOH Na2CO2 + NaHCO3 Na2CO2 + NaOH
V1 = V2 V1 = 0, V2 > 0 V2 = 0, V1 > 0 V1 > V2 V2 > V1
These properties are rare to come from any compound, thus it is usually normal to makes use of less ultrapure compounds as a substitute. A secondary standardization must be made, however, to determine purity of new standard. 7. Explain the rationale behind not storing basic solutions in volumetric glassware.
From experiment, soda ash components are Na 2CO2 and NaOH 5. Is it possible to use NaOH as the primary standard for HCl? NaOH is not a possible standard for HCl since it is highly hygroscopic. It readily absorbs moisture from the air, forming Na2CO3, thus reducing the amount of NaOH 1 that must react with HCl . Therefore, preparation of NaOH solution as primary standard is not possible without resorting to air-and-water free environment to retain known molarity.
Volumetric glassware (or glassware in general) are composed silicic materials which are acidic. These will then react with basic solutions, the latter attacking and dissolving the glass 3 . Long term storage of basic solutions in volumetric glassware will cause etchings in glass and neutralization of the base. 8. Discuss the possible sources of errors and their effect on calculated parameters. Some possible sources of errors that are:
6. Discuss the properties of an ideal primary standard.
The following are some of the important requirements for a primary standard, according to Skoog 2 :
impurities in Na2CO2; and,
primary
standard
end point determination errors (addition of too much or too less HCl titrant)
Absence of hydrate water so that composition of solid does not change with respect to humidity Relatively large MM, such that relative error in weighing the standard is minimized
9. Discuss the cause of carbonate error and its effect on the calculated values
Highly purified
Atmospheric stability
contamination of reagent solutions;
These errors will affect calculations of molar concentration of the soda ash components and the HCl solution. Other sources of errors are parallax error, equipment failure and human error(s).
reaction of base with CO2 forming carbonates;
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on the calculated values obtained in standardization and sample analysis. Carbonate error is an error in endpoint determination due to the presence of carbonic acid in the solution4. Since our solution, initially alkaline in nature, reacts with the carbonic acid, it forms a more neutralized solution, changing the desired pH value. Therefore, values of volume obtained during titration for both standardization and sample analysis will not be accurate. It will affect determination of soda ash sample components since it is highly titrant-volume based.
REFERENCES [1] Stoichiometry in Solution Standardization of Sodium Hydroxide. http://www.macalester.edu/~kuwata/Cl asses/200405/chem%20111/111l%20experiment% 208%20-%20naoh.pdf (accessed June 23, 2016) [2] Skoog D.A., West D.M., Holler J.F. In Introduction to Analytical Chemistry, 8th ed.; Cengage Learning: Pasig, 2012; p 264. [3] Molecular Biology Problem Solver: A Laboratory Guide. Edited by Alan S. Gerstein. A.S., G., Ed.; Wiley-Liss, Inc.: New York, 2001; p 38. [4] Chemistry 3600 Exam Key, 1999. Stephen E. Bialkowski Teaching. http://ion.chem.usu.edu/~sbialkow/Clas ses/3600/Exam2-1999/Exam2-key.html (accessed June 24, 2016).
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