HCL Story (from 7th grade)...

[Krumlink]

I am going to tell you my HCL story, from 7th grade... (really funny and you will probably yell at me )

My science teacher Mr. Dawson and I were good buddies. I would go to his room after school and start messing around with his chemistry stuff because he saw potential in me. One day, he decided it would be a good idea for me to go grab him some baking soda out of the chemistry room. He came with me, and we spent about 2 hours in the chemistry room.

First, I came across some HCL in a METAL ACID CABINET (stupid idea) with some paint chipped off. The lock was so damaged from the fumes, it fell off into peices, leaving me staring at 30% 12M HCL in the cabinet.

I grabbed it and poured about 250ml of it into a flask, while avoiding the fumes erupting from it. I then put the HCL on a bunsen burner to boil some water out of it, to make it more pure . After a while, 5 minutes or so, I then took it off and measured the acidity of it. It was pegging out at 1. I then took it back to his room to experiment.

WHile back in his room, I heated the solution up again and came up with a test: I would put 5 metal strips in 5 different test tubes and pour the HCL into each. There was Zinc, Aluminum, Steel, Brass, and Copper. I poured the solution into each and watched the Zinc and Aluminum start dissolving rather quick. The Copper was partially dissolving also. That was awesome. I then turned to put the cork back in the flask and my labcoat caught the edge of the flask, spilling it all over the chemical resistant desk. The only problem was, was that there was aluminum foil everywhere on the desk, not to mentition his papers he was grading

I ran out of the room, while you could hear everything dissolving. I could hear him say: "WHat did you do now?". Followed by "Holy **** What did you do!!!" I went back in and told him that I spilled the HCL. He then put water on it, which was bad by his part, causing a exothermic reaction. I told him we had to get baking soda or a base chemical, so he poured baking soda all over it. It was now a gooey mushy mess, that was very yellowish green in color. We then had to pour it into a LDPE container and put some chemical stickers all over it. It is still sitting in his closet.



EDIT: Spelling errors

 

[Hero999]

That was a very stupid thing to do, although I can see the funny side.

I take it that he was no longer friends with you afterwards.

Boiling hydrochloric acid would not make it any more concentrated, it would only boil off more HCl gas which would make it weaker not stronger.

 

[audioguru]

He said the hydrochloric acid was only 30% so I guess it was diluted with 70% water. I think boiling it would make it stronger.

 

[Krumlink]

He said the hydrochloric acid was only 30% so I guess it was diluted with 70% water. I think boiling it would make it stronger.

Yes they dillute acids with water.

 

[Omar.M]

Are you guys still friends and such?
Anything happen after that?

Interesting story!
I can happily say that Canadian teachers are a bit more safe =P when letting people sift through the chemicals in the cabinet.

 

[Krumlink]

Yeah we are still friends
He had to take off the assignment because most of it was all messed up.
There was also some sulfur, nitric acid, sulphuric acid, and some other awesome stuff.

 

[Speakerguy]

I blew up a fume hood in high school with ammonium tri-iodide. It's perfectly inert, til it dries out. Then the slightest tap detonates it. Bad ass stuff. Too sensitive to have any real fun with, mostly you will just cause accidents (like I did).

End result was that all inside the fume hood and everything within a 1-2' radius of the hood was stained yellow-purple for the rest of the semester.

ETA: That was me from 9th grade. In 7th I was still playing with KNO3 and sugar.

 

[Krumlink]

Yeah, my friend and I made a PVC model rocket launcher, that you would hold on your sholder and shoot a little rocket out of

 

[Marks256]

I have a pretty interesting story from 7th grade. No where near as dangerous as yours, but i found it pretty amusing (even after i got yelled at repeatedly)

In my 7th grade tech ed class, we were assigned to make a Rube Goldberg machine to close the class room door. So (being the type of person i am), i started thinking of the best way to do it. A few friends and i started looking through the gym equipment closet, and found a nice big 65ish pound yellow punching bag. Actually i think it was 80 lb... i don't remember, but it took about 2-3 of us to move the thing.

So we brought it to the top of the stair steps out side of the tech ed teacher's door, and let it go down it. Because it was a very friction prone object (i think it was like pleather or something), it went really slow. Seeing this as only a minor setback, we ran to the shop, and cut ourselves 2 nice long 2x4 chunks of lumber to use as skids.

Knowing that this would work for a fact, we tested it out (holding it back of course, because we didn't want to wreck the rest of our machine, which started out side the doors at the top of the steps, which as the lockers in it). We were pretty satisfied with the results, except it really didn't reach the door. As a simple last-minute solution, we put a skate board at the bottom of the stairs to make sure the punching bag would make it.

Needless to day, the test results were awesome. When we tested it out, the punching bag started off like a bat out of hell down the stairs. The SECOND it hit the skate board, the door SLAMED shut with a loud crack. So loud that a bunch of people, including teachers, heard it on the other side of the building.

Anyways, the teacher came out of the tech room (seconds after his door slammed shut with enough force to kill a dinosaur), and got all pissed at us.

Let's just say the end result was kind of unjustified. We got the punching bag taken away from us, so we had to completely rebuild our contraption in 2 days.


While he was yelling at us (mostly me, because the punching bag/skids/skate board was my idea), i was thinking to myself "To be fair, we DID close the door...". I was also thinking to myself "Why is that little vein in the side of your neck bulging?", but now i know...



I have attached a google sketchup representation of the setup. Don't laugh at it... for the record, its not proportionate, and some objects are not to scale.

 

[Hero999]

He said the hydrochloric acid was only 30% so I guess it was diluted with 70% water. I think boiling it would make it stronger.

Hydrochloric acid is hydrogen chloride disolved in water and there's a limit to the strentgh of the solution because past a certain concentration it becomes saturated and you can't get any more of the gas disolved in it.

Because the acidity comes from the hydrogen chloride gas which is more volatile than water it will become less acidic when boiled. Try taking some sparkling mineral water, add some universal indicator solution, it'll be a orangish yellow colour indicating a pH of about 4, boil it and it'll go blueish green indicating a pH of about 8.

 

[Krumlink]

Looks really good to me! I cant draw a cube for god sakes

 

[Marks256]

Thanks. I like your new avatar. It is much better than your previous ones...

 

[mneary]

Seventh grade, ca. 1962. Magnesium was (is?) used as an anode to protect water heating tanks, in the form of rods about 9" long and 1" diameter.

One inch piece was darn hard to ignite over a Bunsen burner, but it can be done. Even harder to extinguish; water just makes it burn hotter.

 

[jpanhalt]

Hydrochloric acid is hydrogen chloride disolved in water and there's a limit to the strentgh of the solution because past a certain concentration it becomes saturated and you can't get any more of the gas disolved in it.

True

Because the acidity comes from the hydrogen chloride gas which is more volatile than water it will become less acidic when boiled.

It's a little more complicated than that.

HCl concentrations are often written as weight of HCl per Kg of solution (i.e., wt/wt). By often, I mean by convention what is written on the stock bottle from the manufacturer. Concentrated HCl is about 38% HCl wt/wt or about 451 g HCl per liter (12.4 M). Ignoring for the moment the foolishness of the teacher (at least as recounted by Krumlink), the bottle labeled 30% could be slightly diluted concentrated acid (i.e., 30% wt/wt = 300 g HCl per Kg) or relatively dilute HCl (e.g., 300 mL of concentrated acid diluted to 1 L, which would be about 3.7 Molar).

Now, here's the catch. 3.7M HCl is only about 13% by weight HCl. Upon boiling, HCl in water reaches a constant boiling point, which has a concentration of about 20% by weight of HCl. That is about 6M. This is so-called "constant boiling" HCl, which if carefully done and corrected for atmospheric pressure, is an analytical standard for acid (See: any analytical chemistry textbook of Handbook of Chemistry and Physics).

Thus boiling a solution of HCl can result in either a decrease or increase in concentration of HCl, depending in the starting concentration.

If the story told by Krumlink is accurate, I have little regard for that teacher's judgment and would not trust the label on anything in his laboratory. Therefore, it is uncertain whether boiling the acid solution increased or decreased its concentration of HCl. John

 

[Hero999]

That makes sense, I'm strugling to remember my chemistry, it's something to do with the dynamic equilibrium between the HCl and H2O which varies with pressure and temperature.

 

[jpanhalt]

It has to do with azeotropes. One of the most familiar is the azeotrope of water and ethyl alcohol. That azeotrope boils at a lower temperature than either component (azeotrope = 78.2 C; ethanol = 78.5 C; water = 100 C). So, if you start with a dilute mixture of alcohol in water (say wine), and distill off the alcohol, the lowest boiling fractions -- the first to come off-- will be 95% alcohol. Higher boilng mixtures will come off, until you have mostly water left in the pot. The distillate can be aged to give brandy or scotch, depending on whether you start with wine or grain .

HCl is a bit different. The azeotrope containing 20% HCl (i.e., constant boiling HCl) boils at a higher temperature (108 C degrees) than either component. Thus, if you start with a high concentration of HCl and boil it, the distillate will contain lots of HCl with a little water. The pot will be boiling at less than 108 C but the temperature will increase until the pot has 20% HCl and is boiling at 108 C. Similarly, if you start with a solution containing less than 20% HCl, the distillate will have more water in it. The pot temperature still will be less than 108 C; however, once enough water has distilled for the concentration of HCl in the pot to reach 20%, the temperature will have increased to 108 C, and the distillate will also now have 20% HCl in it.

For more information, see figure 11 in: **broken link removed**

John

 

[Nigel Goodwin]

It has to do with azeotropes.

Well it's educational here! - never heard of that word, and a quick Wikipedia was most informative

All I need now is a suitable conversation to drop it in?

 

[jpanhalt]

This is a great site. You and the other frequent contributors do a lot of work for the rest of us. It's nice to be able to contribute once in awhile.

I can't say I use that word much in polite conversation either. John

 

[Hero999]

What if you put the 20% hydrochloric acid in to a sealed chamber filled with hydrogen chloride gass at a pressure of 2 bar?

Would the water in the acid soak up the gas and become stronger?

 

[jpanhalt]

What if you put the 20% hydrochloric acid in to a sealed chamber filled with hydrogen chloride gass at a pressure of 2 bar?

Would the water in the acid soak up the gas and become stronger?

Is this a trick question? It is actually a question I never considered, as one is usually trying to get the constant boiling acid at something near normal atmospheric pressure in air. I am not an inorganic chemist, so I am just guessing based on intuition that the answer is yes. The concentration of HCl in the solution would increase.

The rationale is that constant boiling HCl in air is relatively constant weight. It is not hygroscopic. The vapor pressure of HCl (actually the HCl-water azeotrope) at room temperature over the 20% solution would be quite low (one reference put it at 11.8 mm Hg); otherwise, it would not be so easily weighed.

Now, imagine the solution is in a closed vessel, you replace the air with HCl, and you maintain a pressure of 1 bar. That is much higher than the vapor pressure of the HCl in the azeotrope, and I would expect the solution to take up some of the HCl. The concentration of HCl in solution would increase.

Now for the tricky part...The question is what happens if the pressure is actually at 2 bar instead of 1 bar. I could not find a table that was free for the partial pressure of HCl over a 20% solution of HCl at 2 bar. We do know it is proportionally higher than at atmospheric pressure, because at higher pressures, the azeotrope contains less HCl, thus the initial distillate from a 20% solution will have proportionately more HCl. But I could not find how much higher it is. From the way your question is written, one can assume the air is replaced with the HCl. Thus, the initial atmospehre is 100% HCl at 2 bar. Although these are non-ideal solutions and deviations from Raoult's law can be pretty large, I can't imagine the vapor phase at just 2 bar would be 100% HCl. Thus, I would expect some HCl to dissolve in the solution to raise the concentration of HCl in the liquid phase.

John