Re: How do you make lava come out from a cardboard volcano?

There are three “standard” laboratory volcanoes.  The first two listed 
below are very dangerous and should only be performed by a skilled chemist 
with appropriate safety measures.  I very strongly recommend the third 
measure listed below.  It is less spectacular but is usually adequate AND 
much safer for the operator and spectators

Permanganate Volcano

The permanganate volcano is based on the reaction between potassium 
permanganate (KMnO4 ) and concentrated sulfuric acid which gives a dark 
green oil (Mn2O7) that undergoes rapid decomposition in the presence of 
moist air to form MnO2 and oxygen.
2 MnO4-(aq) + 2 H+(aq) --> Mn2O7(l) 
2 Mn2O7(l) -->4 MnO2(s) + 3 O2(g) 
There have been several serious accidents with this demonstration. In one 
case, during a practice session prior to class, enough acid was added to 
cover the permanganate completely. When the demonstrator walked to the 
blackboard, the mixture detonated, shattering two panels of the chalkboard 
and spraying reagents over a distance of 40 feet. The demonstrator was not 
injured.  In a second case, however, 15 sixth-grade students were injured, 
two seriously, when this demonstration exploded.

Ammonium Dichromate Volcano

An exciting demonstration volcano can be made with a bit of ammonium 
dichromate. This is a fun science demonstration that takes almost no time 
at all to prepare. Place a small quantity (12 to 15 grams, or half an 
ounce) of Ammonium Dichromate powder on a clay tile. Form the powder into 
a cone shape. Dim the room lights, and light the top of the cone with a 
high heat source such as a propane torch. The ammonium dichromate will 
burn fiercely while producing large volumes of a grayish green ash. Small 
orange sparks will shoot upward a couple of inches. This reaction can be 
incorporated into your papier-mache volcano model like this:  At the top 
of your model, insert either a 30 ml crucible, a jar lid, or some other 
flame-resistant container. Coat your volcano model with a plaster slurry 
to fireproof it, especially near the top of the cone. Place the ammonium 
dichromate in the fire resistant cup at the top of the volcano, and light 
it.  While this demonstration has been used for many years in education, 
some chromium compounds have been found to be carcinogenic. No one can 
eliminate the possibility of contracting cancer. Wash your hands after 
performing the experiment, and use adequate ventilation.
  
Sodium Bicarbonate Volcano - RECOMMENDED

The volcano shape itself is free formed on a sturdy sheet of plywood. Many 
methods can be used, including built up plaster, wallpaper paste, play 
dough (salt dough) and paper-mache. It is built around an empty, open 
bottle, which will form the opening at the top from where the lava 
emerges. Work with it until you get a shape you like. It is good to leave 
some cracks and furrows for your lava to flow through. Decorate as you see 
fit. Once everything is dry and firmly set, it is a good idea to spray it 
with a clear finishing spray to seal it. Put a tablespoon (15 ml) of 
baking soda, a tablespoon (15 ml) of liquid dish soap, and some red (and 
possibly some yellow) food coloring in the jar. Add 1/4 cup (60ml) or so 
of vinegar. It will make a mess, so do it where this doesn't matter so 
much (outdoors). If the "lava" seems a little thick, next time try adding 
some water to the mix before adding the vinegar.