Question

Sheet 23° torr Atmospheric pressure, mmHg 755.0 Temperature of H,O, "C Vapor pressure of H.O at this temperature 21.1 Calculated pressure of CO, in the system, mmHg 733.9 Balanced reaction of NaHCO, and HCl (see Pre-Laboratory Question 4a) = NaHCO, THCL - Null Hi U + CO₂ Trial123 Mass of sample, g 0.1526 0.1526 WL Vinicial mL 14.0ML 38.5 ml 14.0 Maple 37.0 m2 final ml 345 mL A 23.0 22 ZO ValmL (Winal - Vinicial

Experiment 9 Analysis of an Antacid using the ideal gas law.

Calculations:

1) Find moles of CO2

2) Find moles of NaHCO3

3) Find mass of NaHCO3

4) Find mass % of NaHCO3

5) Find average mass % NaHCO3 in Alka-Seltzer

Answer 1

1)

Given Pressure of CO₂ = 733.9 torr = 733.9/760 atm = 0.9656 atm

Volume of CO₂ in trial 1 = 24.5 ml

Volume of CO₂ in trial 2 = 23.0 ml

Average Volume = (24.5 + 23)/2 = 23.75 ml = 23.75 x 10^-3 liters

From ideal gas law, we know that

PV = nRT

Therefore number of moles of CO₂, n = PV/RT

= 0.9656*23.75*10^-3/(0.0821*296.15)   (since R = 0.0821 literatmK^-1mole^-1, T = 296.15 K (given))

Number of moles of CO₂   = 9.54 x 10^-4 moles

2) 1 mole of NaHCO₃ releases 1 mole of CO₂. Therefore,

number of moles of NaHCO₃ = 9.54 x 10^-4 moles

3) Molecular weight of NaHCO₃ = 84.007 g

mass of NaHCO₃ = 9.54 * 10^-4 * 84.007

mass of NaHCO₃ = 8.01 x 10^-2 g

4) Composition of mixture is 325 mg Asprin, 1000 mg citric acid and 1916 mg NaHCO₃  

Mass percentage of NaHCO₃ in the mixture = mass of NaHCO₃ * 100/mass of mixture

= 1916*100/3241

Mass percentage of NaHCO₃ in the mixture = 59.11 %

5) Given mass of the sample = 0.1526 g. Therefore

mass percent of NaHCO₃ determined from ideal gas law= mass of NaHCO₃ * 100/mass of sample

= 8.01 * 10^-2 * 100/0.1526

mass percent of NaHCO₃ from ideal gas law = 52.5%

Possible reasons for difference between the two numbers:

1) experimental errors in measuring pressure and volume of CO₂

2) Assumption that CO₂ behaves like an ideal gas at 23^o C

3) Difference in composition of the particular sample in study to the overall composition of the mixture