Sciencemadness Discussion Board

Please help me avoid killing my students.

electrokinetic - 22-6-2012 at 11:35

My class of 7th graders is going to be dissecting some old carbon zinc batteries. The main issue is the shitload of MnO2 dust that gets everywhere. I read in this post
how to make cleaning the stuff easier by dissolving it with sodium sulfite and acid. I'm planning on using dilute sulfuric acid since using HCl may form Cl2.

But the carbon zinc batteries also contain zinc chloride. How will that affect the situation? Will chlorine gas end up getting formed anyway?

99chemicals - 22-6-2012 at 11:43

I have cleaned up MnO2 dust before with regular lysol multi-purpose cleaner. If you have black counters noboby will notice if you miss a spot.;)

I thought that cleaning up was a very important part of the chemistry lab. Have the students do it!

BiOCl:BoatsInOutCrashLand - 22-6-2012 at 12:13

You seem like a fun teacher. My 7th grade teacher never did that... Oh well.

Pyro - 22-6-2012 at 13:28

according to my teacher lighting a bunsen burner is too dangerous without an hours lecture on safety and loads of safety equipment! keep going on!

MrTechGuy1995 - 22-6-2012 at 14:10

How the hell?
Why don't you just cover the table with a good layer of Cellophane? And force them to wear gloves?

God damn, I would have loved to do that in my 7th Grade year.

Don't worry about the Zinc Chloride, mixing it with Sulphuric acid will only create HCl (vap). But we're thinking to far ahead into this because, you can just wash the ZnCl2 with water, and it shouldn't become a problem.

[Edited on 22-6-2012 by MrTechGuy1995]

peach - 22-6-2012 at 14:38

The main issue is the shitload of MnO2 dust that gets everywhere.

It's not entirely dioxide, a lot of it is activated carbon. I highly recommend you check out the art teacher's supply cupboard and see if they have some sheets of A3 (or bigger) paper in there; if you ask, they may have some they don't really plan on using. Failing that, cut bin / shopping bags in half, use wide tin foil, broadsheet news paper or wide baking parchment to cover the desks. Tape it down. When the lesson is over, those can be folded up and binned rather than scrubbing the desks.

My class of 7th graders is going to be dissecting some old carbon zinc batteries.

You'll need quite a few sets of pliers to get them all off on that. A double lesson here in the UK used to be 1 hour 30 minutes I think. It may take them 30 minutes to get the things open.

The casings aren't particularly hard to open, but they're fiddly, it's easy to break the carbon rod and there may be sharp edges (have some plasters around). If they're not good with their hands, they may also manage to trap a finger in the pliers. But that qualifies for the "now you know" category as far as I'm concerned, like hitting a finger with a hammer when putting nails in.

It would be a good if you demonstrated opening one in front of them first, to show them the best way and that it shouldn't take all lesson.

Go to the top of the can, where the button is located and the lid is crimped on. Gently / firmly, squeeze the sides around the crimped seal. It will begin to distort, rotate the can a bit, squeeze again, go round and squeeze in a few places until the button / lid is loose. Pick / pull it off. Grip the carbon rod and slide that out. You can then try holding the battery upside down (over a dish), tapping the sides to see if the paste will knock out. If not, a wooden skewer (kebab stick) is useful for scraping the paste out; check the spatulas fit if you plan on using those. The splints for bunsens likely won't be strong enough.

If it's proving difficult to get the paste out there are two other options. Grip the (now open) top at the edge, a small bit of it, and peel the casing away like a peel can from the kitchen, rolling it up around the pliers (they need to needle nose for this). Or, give them a beaker and simply drop the battery in there with some water and rinse the paste into the beaker (wash bottles with some water / blunt blade or bladeless syringes + BBQ skewers / kebab sticks would be good). You can find blunt blades at hobby craft places or ebay if you search for glue dispensing etc, as they're used to drop glue for beads / models; also used for brazing flux / braze alloy / solder paste etc. Gen-you-eyen syringe blades, fresh out the pack, end up stuck in fingers too easily. :P

Alternatively, ask the design tech / shop / maintenance guys if they've got a pipe slice / cutter. Slice the casings on all the batteries prior to the lesson (but don't pull them apart) so they can pull the things open at the start and get busy with the chemistry, instead of injuries and shop work. Don't slice the batteries, put them all in a container, then go for break, just in case they overheat in the meantime (take them with you).

Wash the paste by emptying it into a coffee filter paper and pouring water over it.

Don't use hydrochloric to extract the dioxide as the chloride. You will generate chlorine, and quite a lot of it. Even using pencil batteries, the place will start to reek of the stuff and they could start coughing (particularly if anyone has asthma, you may have problems there). I have seen enough chlorine coming off a single lantern battery that there was a visible cloud of it floating around the beaker - that'd probably mean everyone leaving the classroom / hall in a school, it was enough I took the beaker outside myself.

They must wear gloves. Dust masks aren't necessary, since it'll be wet work. Goggles would be an idea, splash wise.

Oooooo..... I think there are about ?3g? in an AA battery, from a very rough memory, so you can work out the rough amount of sulphuric from that. I'd check that prior to the lesson to keep the materials wastage / risk to a minimum. Keep in mind that, if you use sulphuric and you overshoot on the amount, the stuff boils well over 300C, so they won't be able to get a solid out of that; that's far too dangerous for 7th graders to be boiling down. You want to undershoot to make sure you don't have excess sulphuric when going for the solid. You may want to check a few batteries / make sure they're all the same brand / dose the acid out yourself if the plan is to boil down to a solid. If they add too much, boil down and it starts spitting, you've got problems there. It'll be concentrated by that point, 300C+ and, having had it spit at myself, it causes burn marks on contact.

If you can't get the sulphuric amounts under control, it may be safer / easier to go with hydrochloric but have them do that under a fume hood. Mentioning how easy it is to generate dangerous amounts of chlorine from household products around schools kids is generally not a great idea.

Maybe go for the acetate instead.

Also be aware that the salt you get out of the batteries is quite likely to be yellow / brown / black due to iron contamination, which will need explaining as they're usually supposed to be pink.

You can obtain pink product from the batteries, but it's a bit beyond 7th grade. Maybe you could demonstrate it however.

Take about a quarter to a half of your mucky filtrate. Add sodium or potassium hydroxide to precipitate the manganese and iron out. Filter, save the solids in the coffee paper, pour a lot of clean water over them. Add them back to the rest of the mucky filtrate from before, bubbling air through overnight. Filter again. Bingo.... pink. ;)

For the poor achievers, send them to the boiler room to shovel coal. The advanced students can have a go a nuclear reactor.

Your school now owes me seven kagillion dollars for the lesson plan, I'll be inspecting next Sunday at 3.43pm, downgrading the scoring of all staff (for no particular reason) and please ensure the kids are in lessons on my arrival. TRY HARDER NEXT YEAR! :D

[Edited on 23-6-2012 by peach]

blogfast25 - 23-6-2012 at 06:15

Hmmm, let me be the voice of dissent here. The black gunge, which is at least 50 % very fine carbon, is a real pain in the backside and really hard to remove from anything that gets touched by it.

It might be recommendable to do this as a demonstration, for instance on the large, 6 V types:

These contain 4 x 1.5 V cells , neatly compartmentalised in a plastic matrix and the cells do not have any mild steel cladding, making it much easier to break into the cells. The large size also makes them suited for a front-of-class demo on the anatomy of such cells/batteries.

electrokinetic - 23-6-2012 at 14:05

99: Thanks, I'll try it. And the desks ARE black :-)

BIOCI: my 7th grade teacher never had us do anything like that either. He did slap boy students on the ass, though, until Jason Olivarez punched him in the face. Ah, the things we remember about our teachers.

Pyro: Teachers like that suck the life out everything. Don't even get me started on what we're supposed to do if a mercury thermometer breaks. Wait, did I say mercury thermometer? We don't give those to students anymore. No, we keep them all locked up with the plutonium and cyanide where they belong.

TechGuy, valid advice. They do wear gloves, it's more for the tools and desks. I think I'll try your idea on the cellophane.

Peach, I have to admit I may have been misleading. The point of the dissection is really only to see what's inside and to extract the carbon rods so we can use them later for electrolysis experiments. My interest in dissolving the manganese dioxide was really only for cleaning purposes! BUT, lest you fear your effort was for naught, you have now set me on what will no doubt me my new project. No doubt once I get it right, the kids will have a go at it to...eventually. I may need a bit more detailed explanation of what exactly is going on with the filtrate after the KOH gets added and air is bubbled through it though...

Blogfast, YES it is a real pain in the backside! That stuff gets everywhere, rusts everything (no doubt because of the MnO2 mixed in with it), and is a serious pain to get off of anything. Unfortunately a demo won't work, so I'm

MnO2 "dust" or "paste"?

triplepoint - 23-6-2012 at 21:10

I have done a few, I'm hardly an expert, but I have always seen it as a paste that doesn't fly around. It IS very messy, but more like working with damp dirt

AJKOER - 24-6-2012 at 05:50

My advice is to make it a smaller problem by dividing the class into teams. Assign teams on the basis of at least one handy/strong/responsible member to do the team's work.

This should take less time, less material consumed and less to clean up, not to mention lower the likelihood of an accident (some people can't pour water without precipitating a disaster).

It may be a good idea if this is occurring in a place like America to have the worker/team leader sign a release form (contents is a question for one of those legal forums). An even better idea is to float the idea and have another teacher do it first and learn from his/her's experience.

I sincerely wish to thank you for your evident enthusiasm to teach science as in many schools, the focus is not on educating, but on traffic (student) control. For those disputing this claim, lookup where the USA is recently in Science/Math rankings and, even more depressing, where we were.

blogfast25 - 24-6-2012 at 08:02

Quote: Originally posted by triplepoint  
I have done a few, I'm hardly an expert, but I have always seen it as a paste that doesn't fly around. It IS very messy, but more like working with damp dirt

Alkali types are a paste, IIRW. It's a littler easier to handle, that's true.