Sani-Flush®, a commercial toilet bowl cleaner, contains sodium bisulfate (sodium hydrogen sulfate) a — Laboratory Practical / Gas Laws Chemistry Question
Problem Context
Sani-Flush®, a commercial toilet bowl cleaner, contains sodium bisulfate (sodium hydrogen sulfate) and sodium carbonate as its active ingredients. Other ingredients include sodium chloride, sodium lauryl sulfate, talc and some fragrance. Given the information from the manufacturer that the sodium bisulfate is substantially in excess compared to the sodium carbonate, carry out an experiment to determine the percent by weight of the sodium carbonate in a sample of the product.
Give a brief description of your experimental plan.
Model Answer
2HSO4- + CO3 2- → CO2 + H2O + 2SO4 2-
A good plan consisted of weighing a sample of Sani-Flush® and determining the volume of CO2 produced when the sample is added to water.
For example, a good plan might include these steps,
1. Weigh approximately 1 g of Sani-Flush®.
2. Add to syringe.
3. Draw water into the syringe and cover with cap.
4. Determine the volume of gas (CO2) produced.
5. Use ideal gas equation to calculate moles of CO2
6. Convert moles of CO2 to moles of sodium carbonate and then mass of Na2CO3
7. Divide mass of Na2CO3 by sample mass to find percentage.
8. Repeat with second sample.
An average plan was either missing one of these components or had a procedure based solely on the difference in mass. Such a procedure is subject to greater error due to the smaller change in mass relative to the change in volume.
A weak plan had minimal detail about how the experiment would be conducted.
Record your data and other observations.
Model Answer
An example of good work on observations and data recording would be,
1.45 g sample placed in syringe. Set plunger at 5.0 mL. Drew in 14.0 mL of H2O. Gas was evolved and the solution was blue. Plunger reached 47.8 mL after the reaction was complete.
Trial 1: mass Sani-Flush® 2.05 g, initial plunger level 5.0 mL, H2O volume added 14.0 mL, final plunger level 47.8 mL
Trial 2: mass Sani-Flush® 1.60 g, initial plunger level 5.0 mL, H2O volume added 15.0 mL, final plunger level 39.0 mL
Temperature is 23 °C and pressure is 755 mmHg
Show your calculations.
Model Answer
Sample 1: 47.8 - 14 = 33.8 mL
removing water volume: 33.8 mL - 5.0 mL = 28.8 mL gas evolved.
mole of gas: PV = nRT therefore n = PV/RT = = 0.00118 mol CO2
convert to mass: 0.00118 mol CO2 = 0.00118 mol Na2CO3 x (106 g / 1 mol) = 0.125 g Na2CO3
calculate percentage: % = (0.125 g / 2.05 g) x 100 = 6.1%