E8_Mass_Percent_of_NaHCO3_in_AlkaSeltzer - EXPERIMENT 8...

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74 EXPERIMENT 8 Mass Percent of Sodium Bicarbonate in Alka-Seltzer ® Objective: The mass percent of NaHCO 3 in Alka-Seltzer ® will be determined. Introduction: Nearly all manufacturers test selected product samples to ensure their quality. The nature of these quality control tests depends on the product and the means of manufacture. An aerosol air freshener would be evaluated on aroma, liquid dish detergent on its percent water content, a motor oil on its viscosity. In this experiment you will perform a quality control test on Alka- Seltzer ® . The quality control test will involve verifying that an Alka-Seltzer ® tablet contains the manufacturer’s stated amount of active ingredient. Alka-Seltzer ® is one of a number of over-the-counter products used to treat heartburn and acid indigestion. Both heartburn and acid indigestion are the result of excess stomach acid (HCl). Alka-Seltzer ® relieves heartburn and acid indigestion by neutralizing excess stomach acid. The active ingredient of Alka-Seltzer ® that neutralizes excess stomach acid is sodium bicarbonate, NaHCO 3 , a base. When this base reacts with an acid such as HCl, it produces gaseous carbon dioxide, CO 2 , NaHCO 3 ( aq ) + HCl( aq ) NaCl( aq ) + H 2 O( l ) + CO 2 ( g ) (1) If an excess of HCl is used to ensure complete reaction of NaHCO 3 , the moles of CO 2 produced are stoichiometrically related to the moles of NaHCO 3 initially present. The mass of NaHCO 3 can be calculated from the moles of NaHCO 3 . The mass percent of NaHCO 3 can be calculated from the mass of NaHCO 3 and the mass of the sample. The mass of CO 2 produced in Reaction (1) could readily be used to determine the number of moles of CO 2 . But because it is a gas, a direct measurement of the mass of CO 2 is difficult to achieve. However, measuring the volume, temperature, and pressure of a gas can be done with relative ease, and these quantities can be used to calculate the moles of CO 2 . Numerous experiments performed in the seventeenth, eighteenth, and nineteenth centuries led to an empirical description of the physical properties of gases in terms of their pressure ( P ), volume ( V ), number of moles ( n ), and temperature ( T ): PV = nRT (2) where P is usually in atmospheres (atm), V is typically in liters (L), T is expressed in units of kelvin (K), and R is a constant of proportionality termed the universal gas constant (0.08206 atm L/mol K; it has different values with different units, but this is the value pertinent to this experiment). Equation (2) is termed the ideal gas law. As the name suggests, strict adherence to the ideal gas law is the “ideal” case. Such ideal behavior is most commonly observed under
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Experiment 8: Mass Percent of Sodium Bicarbonate in Alka-Seltzer ® 75 conditions of low pressure and high temperature, but even for conditions of 1 atm and 25ºC, approximately those of this experiment, deviations from ideal behavior are negligible for most gases, and use of the ideal gas law is justified. The apparatus shown in Figure 8.1 will be used in this experiment. The reaction
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E8_Mass_Percent_of_NaHCO3_in_AlkaSeltzer - EXPERIMENT 8...

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