Quantitative Analysis of Soda Ash by Double Indicator Method
Quantitative Analysis of Soda Ash by Double Indicator Method
Results and Discussion
The experiment focuses in the use of double indicator titration in quantitative analysis of soda ash sample. Titration refers to the process of measuring the volume of titrant required to reach the equivalnece point. This method of analysis, is based on the chemical reaction
aA + bB → products (1)
where a is the molecules of the unknown substances to be analyzed or the analyte. Analyte reacts with b molecules of B that is the titrant. The titrant is the standard solution which is added from a buret to react with the analyte until the amount of T added equals the amount of A, which is when equivalence point is reached. It is determined through a sudden change in physical property of the solution, such as indicator that changes color in response to appearance of excess titrant. That is however called the end point which is desirable to be as close as possible to the equivalence point.
In this experiment, the analyte was the soda ash sample and the titrant was the HCl which was standardized by a primary standard of known purity, the sodium carbonate. Standardization is the process in which the concentration of solution is accurately determined.
A sample of sodium carbonate with 99.9% purity was dissolved in boiled water and titrated with HCl.
Then, a sample of soda ash was dissolved in boiled water and then, titrated. In a this reaction of HCl with carbonate, the following reactions will take place:
CO32- + H+ → HCO3- (2)
HCO3- + H+ ← H2CO3 (3)
Carbonate ion in aquaeous solutions act as base and is able to accept a proton to form a bicarbonate ion. Bicarbonate ion, upon addition of more HCl then combine to another proton to form carbonic acid.
Solution mixture of the reaction (2) is alkaline while solution mixture in reaction (3) is acidic. In this case, the whole titration should have two breaks in the curve. This is where the use of double indicator is needed.
Results and Discussion
The experiment focuses in the use of double indicator titration in quantitative analysis of soda ash sample. Titration refers to the process of measuring the volume of titrant required to reach the equivalnece point. This method of analysis, is based on the chemical reaction
aA + bB → products (1)
where a is the molecules of the unknown substances to be analyzed or the analyte. Analyte reacts with b molecules of B that is the titrant. The titrant is the standard solution which is added from a buret to react with the analyte until the amount of T added equals the amount of A, which is when equivalence point is reached. It is determined through a sudden change in physical property of the solution, such as indicator that changes color in response to appearance of excess titrant. That is however called the end point which is desirable to be as close as possible to the equivalence point.
In this experiment, the analyte was the soda ash sample and the titrant was the HCl which was standardized by a primary standard of known purity, the sodium carbonate. Standardization is the process in which the concentration of solution is accurately determined.
A sample of sodium carbonate with 99.9% purity was dissolved in boiled water and titrated with HCl.
Then, a sample of soda ash was dissolved in boiled water and then, titrated. In a this reaction of HCl with carbonate, the following reactions will take place:
CO32- + H+ → HCO3- (2)
HCO3- + H+ ← H2CO3 (3)
Carbonate ion in aquaeous solutions act as base and is able to accept a proton to form a bicarbonate ion. Bicarbonate ion, upon addition of more HCl then combine to another proton to form carbonic acid.
Solution mixture of the reaction (2) is alkaline while solution mixture in reaction (3) is acidic. In this case, the whole titration should have two breaks in the curve. This is where the use of double indicator is needed.
References: (1) Hamilton, Leicester Forsyth et.al., Quantitative Chemical Analysis. 12th ed. McGraw-Hill, 1922. (2) John, Mitchell. Organic analysis. Interscience Publishers, 1954. (3) Skoog, Douglas A., West, Donald M., Holler, F. James. Analytical Chemistry An Introduction. 6th ed. USA: Saunders CollegePublishing. 1993. (5) Ott, Lyman. Mendenhall, William. Understanding Statistics. 5th ed. Boston Kent Publishing Company. 1990. 184-189, 250-2 53. MHCl(1)= 2(0.1000±0.0002)(0.999)(0.04450±0.00005)(105.99)=0.0424±0.0114 MHCl(2)= 2(0.1002±0.0002)(0.999)(0.04500±0.00005)(105.99)=0.0420±0.0113 MHCl(3)= 2(0.1002±0.0002)(0.999)(0.04050±0.00005)(105.99)=0.0467±0.0012 AverageMHCl= 0.0424 ±0.0114+ 0.0420 ±0.0113+ (0.0467 ±0.0112)3=0.0437 ±0.0009 %Na2CO3=(Ave. MHCl)(Vph)(MW Na2CO3)g samplex100% %Na2CO3(1)=(0.0437)(0.004 ±0.00005)(105.99)0.0998 ± 0.0002x100%= 18.56 %± 0.0127% %Na2CO3(2)=(0.0437)(0.0041 ±0.00005)(105.99)0.0998 ± 0.0002x100%= 19.06 %± 0.0122% %Na2CO3(3)=(0.0437)(0.003 ±0.00005)(105.99)0.1002 ± 0.0002x100%= 13.87 %± 0.0167% %NaHCO3(3)=0.0437[0.00980±0.0005-(0.0030±0.00005)](105.99)0.1002±0.0002x 100%=31.43% ±0.0106% x = Xn=27.85% ±0.0120%+ 36.20% ±0.0093%+31.43% ±0.0106%3 =31.83% ±0.0185%