Braingle: 'Detention Bound' Brain Teaser

Detention Bound

Science brain teasers require understanding of the physical or biological world and the laws that govern it.

Puzzle ID:	#3642
Fun:	(2.93)
Difficulty:	(1.65)
Category:	Science
Submitted By:	Bobbrt

In a high school science class, Jimmy was given 50 milliliters of water and 50 milliliters of ethanol. His task was to mix them together and then run an experiment on the mixture. When the teacher came to check on him, however, Jimmy's mixture only contained 94 milliliters. The teacher accused him of drinking some of the mixture in an attempt to get intoxicated and immediately sent him to the principal. Jimmy swears that he did not drink the mixture and that he didn't lose any of the liquids by any means. What happened to the other six milliliters, and how could Jimmy prove his innocence?

Answer

When liquids are mixed, the molecules can arrange themselves so that they fit together more tightly than either of the original, pure liquids. A good way to visualize this is to picture a box completely filled with billiard balls (representing large molecules). If you pour a small amount of sand (representing small molecules) into the box, the sand will fill the voids between the billiard balls. The mass in the box will increase, but the total volume will not change. This is how Jimmy could prove his innocence - if he weighs the mixture, it will equal the original weight of the water plus the weight of the ethanol.
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Comments

Mogmatt16 Apr 23, 2002	weird but true- and staright from a book.
cathalmccabe Apr 25, 2002	hmmmmmmm Liquid .... - evapouration
bobbrt Apr 25, 2002	Cath, I believe that the phrase "he didn't lose any of the liquids BY ANY MEANS" covers evaporation. Thank you and have a nice day.
pezda Apr 25, 2002	I find it hard to believe that someone (the teacher) who has run this experiment thousands of times wouldn't know this.
chamber44 Apr 26, 2002	bobbrt, I agree with Cath. Jimmy might not have know that he lost liquids through evaporation so of course he is going to swear it. Have a nice day yourself.
(user deleted) Apr 27, 2002	I'm with pezda - while the puzzle part of the teaser may be accurate and interesting, the scenario in which you placed it is unrealistic.
(user deleted) Apr 28, 2002	If this is what happens when you mix them, how come it didn't happen to all the other kids?
bobbrt Apr 29, 2002	Why are you people so cruel? I just wanted to bring a little splash of joy into everyone's life, and all I get is this vicious, unprovoked abuse. What, oh what, have I done to deserve this brutal tongue-lashing? I think I need a hug...
RyRyRy May 02, 2002	in the answer, it states that all liquids have a smaller volume when mixed...its only miscible liquids that this happens in
Mogmatt16 May 12, 2002	and i dont think it is as drastic as sand and billards balls
frank0001h Jun 01, 2002	I quite agree, bobbrt. They are being most unfair. This was a trainee teacher in her first science lesson. Just the sort of fact that would not be thought of in that situation. I'll give you a hug, (if you're female.)
missie Jun 18, 2002	I'm with you all the way and my joy surged when I read your teaser. I'm angry now because of the unjust cruelty that has ruined my surge of joy.
bobbrt Jun 19, 2002	Why thank you, missie, you're a sweetheart. And Frank, you can keep those hands to yourself. Bobbrt does NOT stand for Bobbie-joe.
dazza Jun 24, 2002	Ever noticed how those that are quickest to criticise a teaser are often those that have never submitted a teaser themselves? I liked it.
missie Jun 25, 2002	And Frank, your wrong. It was a substitute, and the teacher forgot to mention the decrease of volume. Then, the substitue won't get in trouble and neither will anybody else. (In Frank's idea with the trainee teacher the trainee would be in trouble).
missie Jun 25, 2002	And, to those that don't think it would be as drastic with pool balls and sand then how about pool balls and MARBLES.
sk8babe Jul 17, 2002	Hey ignore the bad comments Bobbrt! it's a really gd 1!! and u shud b proud!! rock on!! be happy!! n smile!! =¬D Xx
megan Dec 20, 2002	Im more of a logic fan, but this was interesting too.
jimbo Nov 21, 2003	Good teaser. I'm wondering whether it would be correct to say that the water dissolved some of the alcohol. Nah! That would involve disassociation of some of the molecules. Hmmm?
Bobbrt Dec 11, 2003	Jimbo, this teaser would not work if the water hadn't dissolved the alcohol (or vice-versa). If the two liquids are insoluble in each other, then they wouldn't mix at all and there would be no volume reduction. So yes, there was definitely dissolving involved.
curtiss82 Dec 30, 2003	I think this is a great teaser. Most people don't realize that volumes are not held constant when two different liquids are mixed. And to comment on a previous comment, there are some situations in which the volume increases when two liquids are mixed because of repulsive forces. It so happens that water and ethonal are different sizes and attract each other, thus the volume decreases.
cnmne May 18, 2004	Why the fuss about the scenario? The answer is legitimate. Most of the criticism seems to be directed at the storyline. If all the teasers that contained unusual scenarios or fiction were disallowed, there would be a lot less teasers on this site, including MadAde's (where is Madadia?) and many of mine. A little creativity many times makes a teaser more enjoyable. I wonder how much of the criticism is really the result of not being able to solve the teaser.
WCCope Aug 02, 2007	Jimmbo, it doesn't dissolve the ethanol, it mixes with it. In the example the sand remains sand the balls remain balls, the balls don't turn the sand into sand pool balls (i.e. salt & water make saltwater). That is the definition of miscible (able to mix)
bradon182001 Jul 24, 2010	I think this teaser should be viewed as an educational tool and learn from it. Leave the debating to the politicians. My opinion...
doehead Jul 24, 2010	I still remember these type questions in high school and college. Nice and easy for me,but still a great science question.
auntiesis Jul 24, 2010	Fairly easy, interesting that so many people had to criticize the story. It is just a story around a valid scientific fact. Loved it.
patiencewithaP Jul 24, 2010	Good teaser!
mepapa Jul 24, 2010	i didn't get it , but I am hard pressed to see where anyone's comments were cruel... I also wonder if "bbrobt"? is still with Braingle?
oddrey Jul 24, 2010	I just took an AP chem class yet I never learned this. VERY interesting.
bluemage Jul 24, 2010	This teaser easily draws ire because of the injustice of the situation. A teacher decides to give alcohol to a high school student?? Then he or she is too ignorant to know what happens during an experiment they assigned? And then when the teacher observes something unexpected they decide to jump to conclusions and accuse the student? Accuse them of trying to get drunk off of a miniscule amount of alcohol? Sorry, but thinking about the ways the story sounds so wrong and unrealistic is more interesting than the answer...
cwjakesteel Jul 25, 2010	good teaser. Yes, that's how he could have proved himself innocent, but that doesn't mean that he actually was innocent .
bear01 Jul 25, 2010	nice one.. i worked in a lab and a new technician was baffled for hours trying to make a 70% solution of methanol.. 'the volumes not working" came screaming from the neighbouring prep room..
plenum Jan 13, 2013	Interesting, but think the chemistry teacher would have known.