The set up:
In this exercise, weighed samples of a solid unknown containing
NaCl and NaHCO3 react with hydrochloric acid. The volume
of the CO2 liberated by the reaction in the gas phase is
measured with a gas collection syringe. From the volume we can
calculate the number of moles of CO2 in the gas phase
using the ideal gas approximation.
Since the CO2 is generated in an aqueous environment
(aqueous HCl), some CO2 will dissolve in the liquid
phase. The amount of CO2 dissolved in the liquid phase
is computed using Henry’s Law which requires knowing the partial
pressure of CO2. As described in the exercise, this
requires knowing the entire system gas volume in addition to the
initial and final syringe readings.
The entire system gas volume is the sum of the quantities
labeled Vtube and Vsyr in the diagram below,
corrected for the liquid volume (the aqueous HCl).
The following questions deal with the above data. The appropriate units are specified in the questions. Pay close attention to the number of significant figures in your answers. What is the volume of CO_2 captured in the gas phase (in mL)? What is the number of mmols of CO_2 captured in the gas phase? (Remember to account for the vapor pressure of water.) What is the weight of the sample in grams? What weight of sample (in grams) would be required to produce 35. mL CO_2 (g)? What weight of sample (in grams) that would be required to produce 55. mL CO_2 (g)? When the CO_2 has been completely collected, what is the partial pressure (in atm) of CO_2 (P_CO2) in the system? Assuming the liquid phase (aqueous HCl) is primarily water, what is the concentration (in mol/L) of CO_2 in the liquid phase assuming Henry’s Law (concentration is proportional to partial pressure)? What is the number of mmol of CO_2 in the liquid phase?
The set up: