8 – 1
Mass Percent of Sodium Bicarbonate in Alka-Seltzer
The mass percent of NaHCO
will be determined.
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-
. The quality control test will involve verifying that an Alka-Seltzer
tablet contains the
manufacturer’s stated amount of active ingredient.
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).
relieves heartburn and acid indigestion by neutralizing excess stomach acid.
The active ingredient of Alka-Seltzer
that neutralizes excess stomach acid is sodium
, a base. When this base reacts with an acid such as HCl, it produces
gaseous carbon dioxide, CO
) + HCl(
) + H
) + CO
If an excess of HCl is used to ensure complete reaction of NaHCO
, the moles of CO
are stoichiometrically related to the moles of NaHCO
initially present. The mass of NaHCO
can be calculated from the moles of NaHCO
. The mass percent of NaHCO
can be calculated
from the mass of NaHCO
and the mass of the sample.
The mass of CO
produced in Reaction (1) could readily be used to determine the number
of moles of CO
however, because it is a gas, a direct measurement of the mass of CO
difficult to achieve. In contrast, 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
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
), volume (
), number of moles (
), and temperature (
usually expressed in atmospheres (atm),
in liters (L),
in kelvin (K), and
universal gas constant
K). Equation (2) is termed the
ideal gas law.
the name suggests, strict adherence to the ideal gas law is the “ideal” case. Such ideal behavior is
most commonly observed under 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 between