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Introduction The main objective of this experiment is to find the percentages by mass of Sodium Bicarbonate (NaHCO 3 ) and Sodium Chloride (NaCl) in an unknown mixture, which can be found by chemical means. The mass percentage will verify the purity of a compound. To do this the equation for mass percentage is used; 100% formula weight
ofatomsxatomic weight
x (^) Mass percent is the number of grams of solute in each 100 grams of solution. This lab involved strong acids and bases, which created strong electrolytes to completely ionize in the solution. Acids are substances that ionize in aqueous solutions to form hydrogen ions by increasing the concentration of H+( aq ) ions, and bases are substances that accept H+( aq ) ions when they dissolve in water. The solubility of a substance is by definition the amount of that substance that can be dissolved in a given quantity of solvent. A solution is homogenous mixture, which is a mixture of substances that has uniform composition. The purpose of this lab was to be able to find the amount of Sodium Bicarbonate and Sodium Chloride in an unknown mixture. One of the common laws that scientists use is the concentration law this determines the amount of solute dissolved in a given quantity of solvent or solution. The greater the amount of solute dissolved in a certain amount of solvent, the more concentrated the resulting solution. The unknown mixture and the Hydrochloric acid, once combined, will produce Carbon Dioxide as well as water and salt, then the carbon dioxide will escape the solution that will leave the mixture with Sodium ions and Chlorine ions. The use of strong acids and bases created strong electrolytes to completely ionize in the solution.
Experimentation Before doing the experiment the mass of both reactants must be recorded. The first step to the experiment was to weigh out .5g of Sodium Bicarbonate into five separate test tubes. In order to maintain precision a piece of paper must be placed onto the scale where the compound will be measured. In order to use the correct amount of Hydrochloric acid (HCl) to dissolve the unknown mixture, several trails must be carried out. One mL of Hydrochloric acid) needs to be poured into the first test tube. The resulting reaction needs to be observed and recorded accurately. Secondly, 2mL of Hydrochloric acid need to be poured into the second test tube. The resulting reaction needs to be observed and recorded accurately. Third, 3mL of Hydrochloric acid need to be poured into the third test tube. The resulting reaction needs to be observed and recorded accurately. Fourth, 4mL of Hydrochloric acid need to be poured into the fourth test tube. The resulting reaction needs to be observed and recorded accurately. Fifth, 5mL of Hydrochloric acid need to be poured into the fifth test tube. The resulting reaction needs to be observed and recorded accurately. This part of the procedure of adding one more mL of Hydrochloric acid to the next trial will continue until the Hydrochloric acid completely dissolves the Sodium Bicarbonate in the mixture. The amount of Hydrochloric acid that completely dissolves the Sodium Bicarbonate is the amount that will be used when dissolving the unknown mixture. Thereafter the .5g of the mystery mixture needs to be placed into three separate test tubes. Then the amount of Hydrochloric acid that dissolved the .5g of Sodium Bicarbonate needs to be added to each of the three tubes and the results recorded. Finally
Equation 6: Finds mass of Sodium Bicarbonate (grams) in the unknown mixture with use of the mass of water (grams) X = mass of the water evaporated in grams Y = mass of Sodium Bicarbonate (grams) in the reactants 3 3 3 2 3 2 2 2 1
YgNaHCO molNaHCO gNaHCO molH O molNaHCO gH O molH O XgH O Calculations Calculations made to find the Sodium Bicarbonate mass found in unknown mixture with the use of the Carbon Dioxide mass. Trial 1: 3 3 3 2 3 2 2 2 0.^479 1
- 251 gNaHCO molNaHCO gNaHCO molCO molNaHCO gCO molCO gCO Trial 2: 3 3 3 2 3 2 2 2 0.^208 1
- 109 gNaHCO molNaHCO gNaHCO molCO molNaHCO gCO molCO gCO Trial 3: 3 3 3 2 3 2 2 2 0.^775 1
- 406 gNaHCO molNaHCO gNaHCO molCO molNaHCO gCO molCO gCO Average grams of NaHCO 3 in unknown substance
- (^4873) 3
- 479 0. 208 0. 775 gNaHCO g g g Percent Yield of Sodium Bicarbonate gUnknownMi xture gNaHCO x gUnknownMi xture gNaHCO (^) 3 3 100 % 97. 4 %
- 500
- 487 Percent Error of Sodium Bicarbonate 100 % 9. 25 %
- 4
- 437 3 0. (^43) x gUnknownMi xture gNaHCO gNaHCO Observations:
Table 1 : Observations of Trial Experiments to Determine Amount of Hydrochloric Acid to Use NaHCO 3 (g) HCl (mL) OBSERVATIONS 0.5g 1mL On contact w/ the NaHCO 3 the HCl bubbled up and released. NaHCO 3 and HCl are separate in the test tube w/ a white substance remaining at the bottom of the test tube. 0.5g 2mL Amount of bubbles increase from 1mL. White substance remaining at the bottom of the test tube- 2 compounds separate from each other. 0.5g 3mL Amount of bubbles increase from 2 mL. White substance remaining at the bottom of the test tube- 2 compounds separate. 0.5g 4mL Amount of bubbles increase from 3 mL. White substance remaining at the bottom of the test tube- 2 compounds separate. 0.5g 5mL** (4.7g) Amount of bubbles increase from 4 mL. After bubbles stopped and all gas was released the mixture was completely uniform throughout resulting in a clear liquid. **amount that was chosen for the experiment The experiment was carried out in a series of test tubes in which 0.5 g of NaHCO 3 was mixed with a varied amount of HCl. In the first trial 1 mL of HCl was mixed in with the 0.5g of NaHCO 3. On contact with the NaHCO 3 the HCl bubbled up and released a gas, this trial was unsuccessful resulting in a clear liquid and a white substance that had accumulated at the bottom of the test tube. In the second trial 2 mL of HCl was mixed with 0.5g of NaHCO 3. Like the previous trial this also resulted in bubbles and the release of a gas, likewise it was also an unsuccessful trial resulting in two separate substances in the mixture. In the third trial 3mL of HCl was mixed with 0.5g of NaHCO 3 , this also resulted in the release of a gas, but as before it was unsuccessful due to the two substances that were separate in the mixture. The fourth trial had results like the three previous trials except 4mL of HCl was mixed with 0.5g of NaHCO 3. In the fifth and final
Bicarbonate and Sodium Chloride, the Sodium Bicarbonate quickly ionized into Na+^ and H+^ anions, and CO 3 2-^ cations. Two H+^ anions then attached themselves to a Carbonate anion (CO 3 2-) to produce Carbonic Acid (H 2 CO 3 ). Carbonic acid is unstable if it is in a solution and its concentration is sufficient within the solution. If unstable, as it was in this experiment, Carbonic Acid will decompose into water and Carbon Dioxide (as seen in Equation 3.1). Thus our leaving a solution that contains carbon dioxide, water along with Na+^ and Cl-^ ions. The Carbon Dioxide gas quickly escaped into the atmosphere, leaving a solution of water and Na+^ and Cl-^ ions. The second method to determine the percent composition of a given unknown mixture can be seen in Equation 5.1. When Sodium Hydroxide is added to the mixture it is previously ionized in de-ionized water, due to the Sodium Hydroxide being soluble. The Sodium Hydroxide ionizes into Na+^ and OH-^ ions. Sodium Hydroxide is a base and by definition bases react with H+^ anions. Therefore, the Hydroxide ion quickly reacted with the hydrogen atom in the Sodium Bicarbonate to produce water and Sodium Carbonate (Na 2 CO 3 ). The Sodium Chloride has only ionized in the water to produce Na+ and Cl-^ ions. When heated, the water evaporates leaving a solid mixture of Sodium Carbonate and Sodium Chloride. The average value of the grams of Sodium Bicarbonate in the unknown substance was 0.487g. Our values ranged from 0.208g to 0.775g. Our values were not precise, due to the values not being close to each other. The calculated percent error came out to be 9.25%. This error was largely due to the mixture in the bottle of Sodium Bicarbonate and Sodium Chloride being a heterogeneous mixture. A heterogeneous mixture is a mixture
that does “not have the same composition, properties, and appearance throughout.”^1 In our experiment, when mixed, the Sodium Bicarbonate and the Sodium Chloride were solids. Thus, they did not come together into a homogenous mixture. A homogenous mixture is one that is uniform throughout. The fact that the Carbon Dioxide continues to re-dissolve back into the mixture was also a factor in error. Not all of the Carbon Dioxide returns to the mixture most of it escapes into its surroundings. Another reason that our values were not precise was due to the inaccuracy of the scales. The margin of error for the scale was ±0.0005 grams. The margin of error for the graduated cylinder that was used was ±0.05 milliliters. Any percent error in this lab is attributed to various things. Among them, there exists the margin of the error for the equipment. Also, the room in which the scales were in had many people coming and going, therefore the air in the room was in constant movement, making the scales change the mass values continuously. Conclusion The determination of the percent of mixture of an unknown substance was found. The mixture contained approximately 0.487 grams of Sodium Bicarbonate and 0.013 grams of Sodium Chloride. According to our results Sodium Bicarbonate is approximately 97.4% of the mixture. Therefore, it would be beneficial for the chemical manufacturing company to reduce the purity of this product since 97.4% is a reasonable mixture for Na 2 CO 3 production. However, the actual percentage Na 2 CO 3 of the in the mixture was 80%. Since the actual percentage of the mixture was 80%, it would not be profitable for (^1) Brown, Theodore L, Lemay, H. Eugene, Jr., Bursten, Bruce E., Burdge, Julia R. Chemistry The Central Science. New Jersey: Prentice Hall, 2003.
This chemical reaction will cost the company more money than if they just used the first method. The major uses of Sodium Carbonate are in the manufacture of glass, paper, rayon, soaps, and detergents. It is also used as a water softener, since carbonate can precipitate the calcium and magnesium ions present in “hard” water. Sodium carbonate is also used in the chemical industry to synthesize many different sodium compounds.^3 These uses for Sodium Carbonate are extremely useful in the “real world,” and it should be produced from the mixture by the Chemical Manufacturing Company. (^3) http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/carbonate-uses.shtml
