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Preparation of dry hydrogen?

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LAN_403

2Spoons

Tue May 08 2018, 10:29PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

just be aware that the Al-NaOH method can suffer from thermal runaway. To the point where it starts boiling and then you end up with a balloon full of caustic foam.
A colleague had this happen to him when he was a kid - he was doing this on the bonnet of his dad's car. It did not end well.

klugesmith

Thu Jun 21 2018, 06:04PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

The time had come to open a factory-sealed bag of desiccant granules. Found pink indicator beads mixed in with the product. Package says its contents were silica gel and cobalt chloride.

Internet says pink indicates humidity and blue indicates dryness. So the bag must have had a pinhole, or been permeable and old.

Blueness was restored by overnight baking at about 115 Â°C. Second batch was plenty blue after 2 hours this morning, at barely 100 Â°C.

klugesmith

Sun Jun 24 2018, 04:22AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Got the balloon re-levitated today, after looking up humidity numbers. Moisture's especially significant if the aqueous reaction is allowed to get hot. Sulaiman, you may wish to spot check my numbers here:

For my estimated balloon volume, plus an allowance for flushing gas and spillage, there would be about 0.5 g of water at 30 degrees C or less than 0.1 g at 0 degrees C.

Reaction vessel and chemicals were same as reported before, and once again immersed in a water bath outdoors.
New plumbing includes a bubbler filled with crushed ice and water, then a DIY column with a huge surplus of silica gel desiccant confined between wads of cotton, then an adapter to a plastic soda straw with which the old balloon had been catheterized.

It took about 1/2 hour from first mixing of chemicals to pinching off the balloon. 200 ml of acid in first batch, drained off and replaced with 250 ml more acid for batch 2. 50 g of die-cast scrap was reduced (not in the chemical sense) to 11 g, a loss of 0.6 mol if it were 100% Zn. Generally consistent with the 1/2 mol of H2 in old estimate. I didn't weigh the empty balloon, but the refilled one has a net buoyancy of about 2 grams.
The desiccant column indicator color changed slightly at the very bottom (inlet side).

Now we'll see how long hydrogen keeps the balloon up.

[edit]Must remember that desiccant has one s and two c's, just like analemma has one n and two m's.

Am thinking of measuring the acid concentrations (fresh and spent) by a more precise titration. Looking for suggestions.
Household bases on hand in liquid form are ammonia and drain opener (not sure how well their concentrations are known).
In solid form there's baking soda and lye (not sure how predictable is their hydration state). I suppose the solids could be baked dry before weighing, as with the desiccant granules the other day.

klugesmith

Mon Jun 25 2018, 03:48PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Bringing back childhood memories, I got some pure zinc metal by taking apart batteries. What was left of it, in cells from the b-waste bin. Anybody need some AAA or AA size carbon rods?

Used that to titrate the unknown acid, in a 50 ml beaker, with the indicator being no more bubbles and metal left over. 40 ml of spent acid from balloon job had room for 0.5 g more zinc. 40 ml of "fresh" acid dissolved 4.0 g. That works out to 0.19 and 1.53 mol/L of Zn++.

The useful difference, 1.34 mol/L, closely matches the result from balloon job numbers: 38.9 g metal into 0.45 L of acid -> 1.32 mol/L. So it was fair to regard the die-cast scrap as zinc.

It also tells us that the acid had about 1.53 x 2 = 3.06 mol/L of H+ to begin with. That's 1/4 as strong as muriatic acid from the store. So I must have diluted it with 3 parts of water, not 4, when preparing to de-scale some hot rolled steel many months ago. (not the round parts in Pickling thread here.) Seemed to be a good concentration for well behaved H2 generation.

Couple of other interesting details. The liquid had a strong yellow color, which practically disappeared as the zinc reaction approached its end. And the black debris wasn't just tarry residue from battery zinc. It seemed to grow in dendrite form on the last piece of metal, and it was drawn toward a magnet.

That open vessel of hydrochloric acid didn't spend much time on or around the scale. The system lost a total of about 2.6 g, probably mostly as water vapor and maybe some molecular HCl. At cleanup time, the optical refraction contrast between zinc liquor and plain water was strong.

Plasma

Fri Jun 29 2018, 08:03PM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268

Kludgesmith if you need a high purity Zn source, you can go to a engineering supplier store and ask for glav stick, they are about 10mm square by 300mm,its used by a gas torch to heat steel and the stick is pressed against the hot steel

johnf

Fri Jun 29 2018, 08:34PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Plasma
WRONG
I know you are in NZ and galv stick here is pure zinc with pure indium added so it will stick to steel its also why it is very expensive compared to pure zinc.
The best source of pure zinc is boat anodes as the zinc has to be better than 99% to continue working in saltwaqter properly.
Also plumbers make flashings from pure zinc sheet just ask you will get some offcuts for nix

Plasma

Sat Jun 30 2018, 12:38AM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

Thanks johnf, I wasn't 100% sure of the purity, do you mean calvnic protection...
edit:car radotors are Mg, from a recycling centre you could pick them up for $10

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