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Sodium carbonate (Na2CO3)

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Abstract

Sodium carbonate (Na2CO3), commonly known by trade name soda ash, is a white, anhydrous, powdered or granular material that is an essential raw material used in the manufacturing of glass, detergents, chemicals, and other industrial products. In this experiment, the percent alkalinity of the unknown soda ash sample was determined by titrating it with standard HCl solution.

After three trials, the researchers obtained an average percent alkalinity of 33.20% that resulted to a percent error of 12.63%. The percentage of carbonate and bicarbonate of the same unknown soda ash sample was also determined in the experiment, following the same procedures and using the same titrant that is the standard HCl solution; however, this time, the researchers made use of a pH meter. Subsequently, they acquired 22.44% of carbonate and 26.07% of bicarbonate.

Introduction

Sodium carbonate (Na2CO3), commonly known by trade name soda ash, is a white, anhydrous, powdered or granular material that is an essential raw material used in the manufacturing of glass, detergents, chemicals, and other industrial products [1]. It has a molecular weight of 105.989 g/mol, melting point of 851̊ C (1564̊ F) and a specific gravity of 2.533 [2]. In the year 1998, soda ash was listed as the 11th largest inorganic chemical of all the organic and inorganic chemicals in terms of production, leaving out petrochemical feedstock [3].

In fact, sodium carbonate has already been in production for more than 5,000 years now. It was used by Ancient Egyptians in making glass ornaments and vessels. The product was recovered from dry lake-bed deposits or by burning seaweed and other marine plants. Even the Romans used soda ash for baking bread, making glass and for medicinal purposes. The extraction of sodium carbonate from the ashes of various plants continued until the middle of 19th century and was now popularly known as “soda ash” [1].

There are two ways of processing sodium carbonate. The most common source is trona, a mineral that occurs in natural deposits in evaporated lake beds throughout the world [4]. It is said that the Green Basin of Wyoming is the world’s largest area for naturally-occurring trona [1]. The other source is through Solvay process which is conducted in a lab. Its product is a synthetic sodium carbonate that though possessing the same properties as that found in nature, it’s more expensive and is harmful to the environment [4].

In this experiment, the percent alkalinity as well as percentage of carbonate and bicarbonate of an unknown soda ash sample will be determined. Alkalinity is a measure of the capacity of water or any solution to neutralize or “buffer” acids. This measure of acid-neutralizing capacity is important in figuring out how “buffered” the water is against sudden changes in pH [5].

First, Hydrochloric acid (HCl) will be standardized and will be used as the titrant. An amount of the unknown soda ash sample will be diluted with distilled water and will be used as the analyte. Two titrations will be conducted. The first one is for the analysis of soda ash while the other one is for the analysis of carbonate and bicarbonate in a mixture wherein the researchers will make use of a pH meter. Phenolphthalein and methyl orange are the indicators that will be used.

Titration is a volumetric technique where the titrant is added into the analyte until the equivalence point is reached. Equivalence point is the point at which an exactly right amount of titrant has been added in order to stoichiometrically react with the analyte. The equivalence point may be signaled by the change in color of the analyte. The color may vary depending on the indicator used. Also, the equivalence point may be obtained using the titration curve [6].

In this experiment, the reporters made use of sodium hydroxide, hydrochloric acid, and sodium carbonate or soda ash. Sodium hydroxide causes eye damage and severe skin burns, hydrochloric acid is very hazardous in case of skin contact (corrosive, irritant, and permeator) and in case of eye contact (irritant and corrosive), in contrary, sodium carbonate is not classified as toxic but can injure the eyes and irritate the skin upon contact and be harmful if ingested, hence, extra care must be observed in handling these chemicals [7] [8] [9]. This experiment includes the determination of the percent alkalinity as well as the percentage of carbonate and bicarbonate in an unknown soda ash sample. Experimental Section

A.Chemicals and Reagents

In the analysis of soda ash, the reporters made use of impure Na2CO3 (soda ash), standard (0.10M) NaOH, concentrated HCl, methyl orange, and distilled water. They also used an analytical balance, 250-mL flasks, acid/base buret, iron stand, buret clamp, graduated cylinder, stirring rod and transfer pipette. In the volumetric analysis of a carbonate-bicarbonate mixture, the researchers made use of the same unknown soda ash sample and standardized HCl solution from the analysis of soda ash. They also employed phenolphthalein and methyl orange indicators in the experiment. Acid/base buret, beakers/flasks, stirring rod, wash bottle, pH meter, and analytical balance were the materials utilized. B.Preparation of 0.10 M HCl

Solution

In order to prepare a 0.10M HCl, the researchers cautiously and slowly allowed 4.2 ml of concentrated HCl to flow along the wall of the beaker containing 500.0 ml of distilled water. After which, they transferred this solution into a labeled storage bottle. C.Standardization of 0.10 M HCl

Solution

Since the standardization required exact amount of solutions, the researchers made use of two burets. The first buret was used to transfer 20 ml of standard NaOH solution (from Analysis of Lactic Acid in Milk) to a beaker/ flask, while the other buret was filled with the acid to be standardized. They titrated the NaOH solution containing three drops of methyl orange indicator with the acid until it turned orange. Then, they computed for the molarity of the acid. D.Determination of Total Alkalinity of the Soda Ash

The researchers dissolved 0.3000 g to 0.6000 g of the unknown soda ash sample in 150 ml of distilled water. They transferred this solution into a 250-mL volumetric flask diluting it with distilled water. The solution was then mixed thoroughly by inverting the volumetric flask for several times. They added three drop of the methyl orange indicator to the 50.0 ml aliquot of the solution and titrated it with the standard acid until endpoint. The percent alkalinity of the unknown soda ash was later computed. E.Analysis of the Carbonate-Bicarbonate Mixture

First, the researchers rinsed the electrode of the pH meter with distilled water, dried it and immersed it into the buffer to calibrate the pH meter. Next, they filled up a buret with standard HCl, the titrant, and recorded the initial volume. Then, they dissolved the 2.000 g of solid sample in 100 ml of distilled water and transferred the resulting solution into a 250-mL volumetric flask. The said solution was diluted to the mark and was thoroughly mixed by inverting the flask for several times.

After that, the researchers added three drops of phenolphthalein into 50.0 ml aliquot of the solution. The electrode of the pH meter was then dipped into the solution and titrated with the acid. They recorded the volume of HCl once the solution turned light pink and later added three drops of methyl orange indicator. Once more, they titrated the solution until endpoint and recorded the volume of HCl. The data gathered were used to compute for the percentage of sodium carbonate and sodium bicarbonate.

Results and Discussion

The standardization of hydrochloric acid that will be used for all the titrations was the first thing to do in this experiment. In its standardization, it was made to react with standard sodium hydroxide; hydrochloric acid was used as the titrant while sodium hydroxide acted as the analyte. It’s preferable to titrate NaOH with standard HCl rather than the reverse process for HCl is more stable than NaOH since NaOH tend to absorb atmospheric carbon dioxide that changes its concentration. HCl + NaOH NaCl + HOH

Figure 1- Equation of the standardization of the titrant

Figure 1 shows the reaction of one mole of hydrochloric acid and one mole of sodium hydroxide. When the two solutions react, it will produce one mole of sodium chloride and one mole of water. Standardization of HCl

Trial 1Trial 2
Vol of NaOH20 ml20 ml
Vf HCl20.3 ml20.2 ml
Vi HCl00
Vol of HCl used20.3 ml20.2 ml
M NaOH0.0926 M0.0926 M
M HCl0.0912 M0.0917 M
Ave M HCl0.0915 M

Table 1- Data and Results for Standardization of NaOH
Trial 1
0.0926mol NaOHx0.020 Lx1 mol HClx1000 ml=0.0912mol HCl
L1 mol NaOH20.3 mlL
Trial 2
0.0926mol NaOHx0.020 Lx1 mol HClx1000 ml=0.0917mol HCl
L1 mol NaOH20.2 mlL

Average Molarity
0.0912mol HCl+0.0917mol HCl
L L=0.0915mol HCl
2L

Table 1 shows all the data gathered in the standardization of HCl as well as the necessary computations. In the first trial, the researchers obtained 0.0912 M of HCl and on the second trial, 0.0917 M of HCl. The average of two trials which was used in all of the remaining computations in the experiment was calculated to be 0.0915 M of HCl. Alkalinity of Soda Ash

Trial 1Trial 2Trial 3
Mass of Sample0.314 g0.314 g0.314 g
Vf HCl4.1 ml8.7 ml12.9 ml
Vi HCl04.1 ml8.7 ml
Vol of HCl used4.1 ml4.6 ml4.2 ml
Mass of Na2CO30.0994 g0.1115 g0.1018 g
% Alkalinity31.66%35.51%32.42%
Ave % Alkalinity33.20%
% Error12.63%

Table 2 – Data and Results Alkalinity of Soda Ash
Trial 1
0.0915mol HClx4.1 mlx106 g Na2CO3x250 ml=0.0994 g Na2CO3
L10002 mol HCl50 ml

% Alkalinity=0.0994 g Na2CO3x100=31.66%
0.314 g sample

Trial 2
0.0915mol HClx4.6 mlx106 g Na2CO3x250 ml=0.1115 g Na2CO3
L10002 mol HCl50 ml

% Alkalinity=0.1115 g Na2CO3x100=35.51%
0.314 g sample

Trial 3
0.0915mol HClx4.2 mlx106 g Na2CO3x250 ml=0.1018 g Na2CO3
L10002 mol HCl50 ml

% Alkalinity=0.1115 g Na2CO3x100=32.42%
0.314 g sample

Average % alkalinity=31.66%+35.51%+31.42%=33.20%
3

% Error=38%-33.20%x100=12.63%
38%

Table 2 shows the data acquired as well as the essential calculations in the analysis of soda ash. In the first trial the researchers got 31.66% of alkalinity, 35.51% in the second trial, and 32.42% in the last trial
resulting to an average of 33.20% of alkalinity. Soda ash’s theoretical percent of alkalinity is 38% which means to say that the researchers committed 12.63% of error.

Trial 1Trial 2Trial 3
Initial Volume0.000.000.00
Vol H2Ph endpt9.3 ml9.2 ml9.4 ml
Vol MO endpt32.3 ml32.332.3 ml

Table 3- Data and Results for Volumetric Analysis of the Carbonate-Bicarbonate Mixture

Percent Na2CO3 in the Sample
Trial 1
18.6ml HClx1 Lx 0.0915 M HClx1 mol Na2CO3x106 gx250 ml=0.45 g Na2CO3
1000 ml2 mol HClmol Na2CO350 ml

Trial 2
18.4ml HClx1 Lx 0.0915 M HClx1 mol Na2CO3x106 gx250 ml=0.45 g Na2CO3
1000 ml2 mol HClmol Na2CO350 ml

Trial 3
18.8ml HClx1 Lx 0.0915 M HClx1 mol Na2CO3x106 gx250 ml=0.46 g Na2CO3
1000 ml2 mol HClmol Na2CO350 ml

% Na2CO3 =0.45 g+0.45 g+0.46 g
3 x100=22.44%
2.0202 g

Percent NaHCO3 in the Sample
Trial 1
13.7ml HClx1 Lx0.0915 M HClx1 mol NaHCO3x84 gx250 ml=0.52 g NaHCO3
1000 ml1 mol HClmol NaHCO350 ml

Trial 2
13.9ml HClx1 Lx0.0915 M HClx1 mol NaHCO3x84 gx250 ml=0.53 g NaHCO3
1000 ml1 mol HClmol NaHCO350 ml

Trial 3
13.5ml HClx1 Lx0.0915 M HClx1 mol NaHCO3x84 gx250 ml=0.52 g NaHCO3
1000 ml1 mol HClmol NaHCO350 ml

% NaHCO3 =0.53 g+0.52 g+0.53 g
3 x100=26.07%
2.0202 g

The needed data and computations are all provided in Table 3. The researchers performed three trials for the analysis of carbonate-bicarbonate mixture. The average of these three trials was computed so as to obtain the percentage of sodium carbonate and sodium bicarbonate in the sample. Consequently, the researchers got 22.44% of sodium carbonate and 26.07% of sodium bicarbonate.

Figure 2 – Titration curve for the Analysis of the Carbonate- Bicarbonate Mixture

In figure 2, two breaks are seen in the titration curve for the analysis of the carbonate-bicarbonate mixture. These breaks serve as a proof to the two-step neutralization process. The break at the first equivalence point is not that defined as compared to the break at the second equivalence point, hence, the first equivalence is not recommended for highly analytical work. Sodium carbonate is the principal specie in the solution at the midpoint of the first break while the second equivalence point corresponds to the formation of the sodium bicarbonate.

Phenolphthalein and methyl orange were the indicators used in the analysis of the carbonate-bicarbonate mixture. The equivalence point pH for the first reaction occurred between pH 8 and 9, thus, phenolphthalein is a suitable indicator to be used. Aside from phenolphthalein, thymol blue which has a pH range of 8.0 to 9.6 may also be used as an alternative. On the other hand, methyl orange was utilized for the second reaction because the equivalence point pH at that reaction took place between pH 4 to 5.

References

INTERNET RESOURCES
1.About Soda Ash. (2013, February 25). Retrieved from http://www.ansac.com/products/about-soda-ash/ 2.General Chemical and Industrial Products. (2013, February 25). Retrieved from http://www.genchem.com/properties.asp 3.Soda Ash. (2013, February 25). Retrieved from http://minerals.usgs.gov/minerals/pubs/commodity/soda_ash/ 4.What is Soda Ash?. (2013, February 25). Retrieved from http://www.wisegeek.org/what-is-soda-ash.htm 5.Alkalinity. (2013, February 25). Retrieved from http://water.me.vccs.edu/exam_prep/alkalinity.html 6.Titrations. (2013, February 25). Retrieved from http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Titrations-875.html 7.First Aid, Safety Precautions, and Specifications for Lye (Sodium Hydroxide) and Caustic Potash (Potassium Hydroxide). (2013, February 25). Retrieved from http://www.certified-lye.com/safety.html 8.Hydrochloric acid MSDS. (2013, February 25). Retrieved from https://www.sciencelab.com/msds.php?msdsId=9924285 9.Titration. 2013, February 25). Retrieved from http://www.titrations.info/acid-base-titration-solutions

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