Sciencemadness Discussion Board - Magnesium and Silver(I) Nitrate

Magnesium and Silver(I) Nitrate

Volanschemia - 30-1-2015 at 00:57

I just did the Magnesium and Silver Nitrate deflagration the other day. Such a great reaction, and it's produced the brightest flash out of all my combustion reactions (besides thermite perhaps).
It's also leaves a fantastic black mark behind. Am I right in thinking that's tiny silver particles?

I set up my own dripping apparatus out of a bottle, some vinyl tubing and an inline tap as I don't have a burette (and if I did it wouldn't be sitting over an explosion site). I will post some pictures soon.

Sources: File Attached (Found on the Internet)

Stoichiometry: I used 0.5g of 500 mesh Magnesium Powder and 1.2g of Silver Nitrate that was ground in a mortar and pestle and then thoroughly dried in an oven.

The reaction: 2AgNO₃ + Mg = Mg(NO₃)₂ + 2Ag

PS. As a side note, how many people on here have worked with silver compounds and gotten silver stains on your hands? They seem to be very hard to avoid. I was wearing gloves and I still somehow got some small black dots on my hands!

PPS. Just noticed that spell check doesn't recognize 'Deflagration', 'Thermite', or 'Burette'.

Attachment: Displacement of magnesium with silver nitrate.doc (71kB)
This file has been downloaded 5023 times

[Edited on 30-1-2015 by TheAustralianScientist]

Dornier 335A - 30-1-2015 at 04:02

I have tried it. I used freshly milled 20 µm magnesium powder and mixed it very well with silver nitrate just before use. I must say that I was scared of premature ignition because I didn't actively dry the silver nitrate beforehand. Nothing bad happened though and the mixture exploded with a deep POOF when touched with a wet stick. I did not experience it as particularly bright, but that might be due to it's incredible burn speed. It was faster than most other flash powders I've made. The tests can be found here: https://www.youtube.com/watch?v=RcflI_gQMYA
I too got those small black dots on my hands...

simply RED - 30-1-2015 at 05:57

Excuse me, Dornier, it is not on the topic, but you present a graphic in one of your videos (lost link) that you made flash powder with energy content 12 MJ/kg. May you post the composition and how you calculated this?

Dornier 335A - 30-1-2015 at 07:35

I suppose you're referring to my report compositions video? That would be Mg/NaNO₃ flash powder. I used 55% Mg and 45% NaNO₃, the ratio I've found to burn the fastest. I can't remember how I calculated it in the video so I'll do it again.

2 NaNO₃ + 8 Mg → Na₂O + 5 MgO + N₂ + 3 Mg(g)
3 Mg(g) + 1.5 O₂ → 3 MgO

The total molar weight of the reactants is 279.44 g.
The ∆H of the first one is: 5*(-601.8)+(-416)-(2*(-467)) = -2491 kJ
And for the full reaction including the secondary combustion:
8*(-601.8)+(-416)-(2*(-467)) = -4296.4 kJ

2.491 MJ/mol / 0.27944 kg/mol = 8.9 MJ/kg
4.2964 MJ/mol / 0.27944 kg/mol = 15.4 MJ/kg

In a detonation only the first reaction would have mattered but in this case (testing report compositions) the secondary, thermobaric reaction adds to the sound and is relevant.

simply RED - 30-1-2015 at 09:13

Indeed, it can't be without using oxygen from the air. Thanx.

Bert - 30-1-2015 at 09:28

OP: Edit to show your sources of information, give stoichiometry, generally try to describe experiment more precisely.

Then this can go back into EM.

(Edit)

THANKS! back to EM-

Yes, it can go off before you're expecting. Keep quantities SMALL.

[Edited on 31-1-2015 by Bert]

Fulmen - 30-1-2015 at 09:35

Silver nitrate is also a simple qualitative test for pure/alloyed Mg. It will instantly produce a black spot on pure Mg but not on any of the common alloys.

Bert - 30-1-2015 at 10:00

Yes-

A quick, cheap test for high % Mg presence in alloy: Just file or sand a small area clean, then brush on common white vinegar (5% acetic acid). High Mg alloys will quickly bubble, Al won't.

blogfast25 - 30-1-2015 at 10:19

Quote: Originally posted by Dornier 335A

2 NaNO₃ + 8 Mg → Na₂O + 5 MgO + N₂ + 3 Mg(g)

The reduction of Na2O with Mg is also thermodynamically favourable:

Na2O + Mg === > 2 Na + MgO

∆H<sub>reaction</sub> = - 602 -(- 418) = - 184 kJ/mol (NIST values for ∆H<sub>formation</sub> of the reagents)

This reaction has also been carried out in practice and reported here, but using NaOH instead of Na2O.

[Edited on 30-1-2015 by blogfast25]

Bert - 30-1-2015 at 16:36

Fine unoxidized Mg powder is so much fun, it just lends itself to the more spectacular chemistry demos... There was a time it was included in kid's hobby chemistry sets. No more, at least in USA.

Try not to lose any fingers, and wear safety glasses that stop UV light. I made the mistake of looking at such reactions from way too close without proper eye protection as a teen.

A mixture of Mg and finely powdered PTFE (Teflon) is energetic, and a bit safer on a humid day- POOF!

Volanschemia - 30-1-2015 at 17:49

Quote: Originally posted by Bert

Fine unoxidized Mg powder is so much fun, it just lends itself to the more spectacular chemistry demos... There was a time it was included in kid's hobby chemistry sets. No more, at least in USA.

Try not to lose any fingers, and wear safety glasses that stop UV light. I made the mistake of looking at such reactions from way too close without proper eye protection as a teen.

A mixture of Mg and finely powdered PTFE (Teflon) is energetic, and a bit safer on a humid day- POOF!

Thankyou.
New to the forum so still some learning to be done.

I might have a look at PTFE/Mg flash powder. Looks pretty fun!

Yes, it's a shame about the demise of the chemistry set. Most of them now proudly proclaim "NO CHEMICALS". :mad:

[Edited on 31-1-2015 by TheAustralianScientist]

PHILOU Zrealone - 31-1-2015 at 12:51

During the explosion, due to the heat of reaction, Mg(NO3)2 isn't present anymore
So
2AgNO3 + Mg ==> Mg(NO3)2 + 2Ag

becomes
2AgNO3 + Mg ==> MgO +N2 + NxOy + N2 + 2 Ag
(and maybe some Mg3N2)

[Edited on 31-1-2015 by PHILOU Zrealone]

Molecular Manipulations - 31-1-2015 at 13:15

Why not:

2 Ag(NO₃) + 6 Mg → 2 Ag + 6 MgO + N₂

Magnesium can easily reduce any nitrogen oxide, so only if silver nitrate is in great excess will any nitrogen oxides form.

[Edited on 31-1-2015 by Molecular Manipulations]

Photos

Volanschemia - 1-2-2015 at 21:12

As promised, here are some photos of my dripping setup.

I have a desk three levels. There is a soft drink bottle with some water in it and a pipe glued in the bottom with Araldite. The pipe goes through a hole in the top level and is attached to an inline tap glued into position so it lets a drop of water through every 15 seconds. Some more pipe is attached to the other end of the inline tap and dangles over the spot where the mix will be placed. While setting up, the bottle is on the middle level so water cannot get to the tap. When I am ready for the reaction, I move the bottle up onto the top level on top of a bucket and a dog food tin and the water runs through the pipe to the tap. 15 seconds later: POOF!

Trotsky - 4-2-2015 at 06:03

Is this blend shock sensitive? I've seen lots of videos over the years of water being used to initiate the reaction, but I've always wondered if hitting it with a hammer would do. I assume so, but I've not seen it done.

Fulmen - 4-2-2015 at 06:21

Any composition containing magnesium metal should be considered highly sensitive to shock ,friction, heat, insults and foul language.

Wizzard - 4-2-2015 at 17:14

Maybe anecdotal, but I avoid silver stains by keeping out of the sun / UV light sources, and soaking with a very mild base (milk works OK, heavy soap also works). Usually comes off enough that the stain (still present) is hardly visible.