A 5.0-L air sample containing H2S at STP is treated with a catalyst to promote the reaction, H2S + O2 = H2O + S(solid). If 3.2 g of solid S was collected, what is the volume percentage of H2S in the original sample?
The concentration H₂S is 45 % (v/v).
Step 1. Write the balanced chemical equation.
2H₂S + O₂ → 2H₂O + 2S
Step 2. Convert grams of S → moles of S → moles of H₂S
3.2 g S ×
Step 3. Use the Ideal Gas Law to calculate the volume of H₂S at STP.
Step 3. Calculate the concentration of the H₂S.
Percent by volume =
Note: The definition of Standard Pressure was changed to 100 kPa in 1982.