Confusing Stoichiometry Question

AI Thread Summary
The discussion revolves around a chemistry problem involving the production of chlorine gas (Cl2) through a reaction with potassium permanganate (KMnO4) and hydrochloric acid (HCl). In part A, the correct mass of KMnO4 needed to produce 2.5 L of Cl2 gas at standard temperature and pressure (STP) is calculated to be 7.05 g. However, there is confusion regarding the calculations for part B, which requires determining the volume of commercial hydrochloric acid needed, given its concentration and density. Participants highlight the importance of verifying numerical answers against expected values and using the ideal gas law for accuracy. There is also a note on the misinterpretation of the density of chlorine, which contributed to the initial calculation errors. The discussion emphasizes the need for careful calculations and checks in chemistry problem-solving.
pure kirk
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I got this question as an example question and I have no clue on how to solve part B

Chlorine can be produced by the reaction:
2KMnO4 + 16HCl ->2KCl + 2MnCl2 + 5Cl2 + 8H2O
(a)What mass of KMnO4 is required to produce 2.5 L of Cl2 gas measured at STP?

For part A I got 7.05 g ( 0.044615 moll)
(b) Calculate the volume of commercial hydrochloric acid required (Commercial grade hydrochloric acid is 36.0% HCl by weight, and has a density of 1.18 g mL^(–1)).
 
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pure kirk said:
I got this question as an example question and I have no clue on how to solve part B

Chlorine can be produced by the reaction:
2KMnO4 + 16HCl ->2KCl + 2MnCl2 + 5Cl2 + 8H2O
(a)What mass of KMnO4 is required to produce 2.5 L of Cl2 gas measured at STP?

For part A I got 7.05 g ( 0.044615 moll)
That is much too low. Please show your calculations.

pure kirk said:
(b) Calculate the volume of commercial hydrochloric acid required (Commercial grade hydrochloric acid is 36.0% HCl by weight, and has a density of 1.18 g mL^(–1)).
Can you start by figuring what mass of HCl you need?
 
DrClaude said:
That is much too low. Please show your calculations.

I got 7.051 g as well:

 
Last edited by a moderator:
I'm sorry for the mistake. I used the density of Cl2 given by WolframAlpha, which is much higher.
 
Looks like they are listing density of a liquid Cl2 - which doesn't make much sense at STP...
 
Borek said:
Looks like they are listing density of a liquid Cl2 - which doesn't make much sense at STP...

Indeed. Very strange.

I feel ashamed because I didn't follow the rule that I always tell my students: when you get a numerical answer, always try to figure out if the order of magnitude makes sense. I should've checked with the ideal gas law...
 

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