September 17, 2021, 06:35:50 AM
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### Topic: Crime Scene Mystery (I don't know how to solve it or which formulas to use)  (Read 591 times)

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#### LarrysTrendyFoods

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##### Crime Scene Mystery (I don't know how to solve it or which formulas to use)
« on: July 28, 2021, 08:11:45 AM »
Welcome to the crime scene:
- The victim of the crime was found at the bottom of a pool
- The pool is cylindrical and is 12.0m wide and 8.00m deep.
- The body looks badly burnt.
Your partner states, "The victim seems to have caught on fire and jumped into the pool to put it out. Likely cause of death is by drowning."
However, you, as an experienced detective and expert in the field of chemistry still have questions: There is no sign of combustion - where did the fire come from? You ask the crime scene investigator (CSI) to run a sample of the pool water before letting anybody remove the body from the pool.
The results are returned, and the pool is found to be highly basic, with a pH of 12, and an OHâˆ’ concentration of 1.0 x 10^-2 mol/L. You are told the pH of regular pools is about 7.1 and you realize the body was not burned before entering the pool, but after...
You send an order to remove the body from the pool, but the CSI agent interjects, stating that the pH levels make the pool too dangerous. However, it would take too long to drain the pool, as the body needs to be examined as soon as possible. The CSI agent suggests that the pool could be neutralized by adding vinegar from a nearby store. She asks one of the officers to go and buy ten 4-L jugs of vinegar, with a pH of 2, stating that it should be enough to bring the pH down to 7.
You want to double-check her estimation before sending your officer to the store.
a) Using your knowledge of acids and bases, verify whether the CSI agent is correct or incorrect by using calculations and showing your full solution.
b) You also want to avoid wasting any vinegar if necessary. Depending on your answer from part (a), how many liters of vinegar would be unused OR how many additional liters of vinegar would be required to neutralize the pool.

#### Borek

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##### Re: Crime Scene Mystery (I don't know how to solve it or which formulas to use)
« Reply #1 on: July 28, 2021, 08:58:57 AM »
Question tries to be interesting, but the chemistry used is even less realistic than the story

It is about concentrations and pH of weak acids. Do you know how to calculate pH of a weak acid solution, or how to do reverse calculation to find concentration of the acid from its pH?
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#### Corribus

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##### Re: Crime Scene Mystery (I don't know how to solve it or which formulas to use)
« Reply #2 on: July 28, 2021, 10:56:04 AM »
That is an amusingly long introduction to what turns out to be a basic (ha!) neutralization problem. Kinda disappointed after all that preamble. Thought I was gonna get to solve a murder mystery.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

#### LarrysTrendyFoods

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##### Re: Crime Scene Mystery (I don't know how to solve it or which formulas to use)
« Reply #3 on: July 29, 2021, 09:02:31 PM »
Question tries to be interesting, but the chemistry used is even less realistic than the story

It is about concentrations and pH of weak acids. Do you know how to calculate pH of a weak acid solution, or how to do reverse calculation to find concentration of the acid from its pH?

Unfortunately no, but can you go over the steps if you don't mind
Thank you!

#### Borek

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##### Re: Crime Scene Mystery (I don't know how to solve it or which formulas to use)
« Reply #4 on: July 30, 2021, 04:11:14 AM »
That's not how the forum works.

You can try to start here: https://www.chembuddy.com/?left=pH-calculation&right=pH-weak-acid-base

or just google "weak acid pH calculation".
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#### LarrysTrendyFoods

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##### Re: Crime Scene Mystery (I don't know how to solve it or which formulas to use)
« Reply #5 on: July 30, 2021, 07:30:32 AM »
That's not how the forum works.

You can try to start here: https://www.chembuddy.com/?left=pH-calculation&right=pH-weak-acid-base

or just google "weak acid pH calculation".

I'm sorry, but yeah sure I'll check it out thank you so much!