Hydrogen gas can be produced by reaction of caustic soda with
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demonstrations is the combustion of hydrogen in a balloon. It has all the qualities desirable in a flashy experiment, and the actual execution is exceptionally easy – the difficulty, however, comes down to obtaining the hydrogen gas if none is available. This procedure is meant to be conducted in a lab (e.g. at a high-school level) where hydrogen isn’t available (typically because of safety restrictions regarding storing hydrogen on the premises).
While there are many easy ways of generating small quantities of hydrogen gas (e.g. zinc in hydrochloric acid), filling a balloon requires two key aspects – firstly, a reasonably large quantity (several litres), and secondly a somewhat high pressure, which are not as commonly seen.
The procedure below involves mixing aluminum powder with a concentrated sodium hydroxide solution and bubbling the resulting gas through water to cool and purify, before capturing the gas in a balloon.
Safety Notes
Warning: this reaction, in the form presented below, is not exactly friendly – proceed at your own risk
Perform this reaction in a fume hood if possible
The initial reaction produces a minimum of fumes, but excess hydrogen may be vented; additionally, there is a risk of the (hot, caustic) reaction product spilling and the balloon bursting/exploding.
Ensure you use a Pyrex/Kimax flask
The reaction is highly exothermic and a regular glass flask will shatter at the peak of the reaction
Wear gloves
Part of this procedure requires holding the flasks during the reaction – you will be maintaining the seal manually and there is a high chance that you will get hot, concentrated sodium hydroxide on your hands.
Wear goggles (and possibly a lab coat)
This reaction has a risk of explosion, and uses extremely caustic chemicals that will reach very high temperatures during the reaction.
Avoid sources of static electricity (e.g. sweaters)
The balloon, once filled, can explode unexpectedly, especially if exposed to small electrical discharges.
Note: this is a violent reaction – it takes a moment to get going, but accelerates rapidly – the products are extremely hot. If necessary, you can slow the reaction down by immersing the reaction flask in a container of cold water for the duration of the reaction.
Materials
Note: quantities are approximate.
100-125mL of concentrated (~18M) sodium hydroxide solution
2mL of aluminum powder (about 2cm in a standard test tube)
2 Erlenmeyer flasks (250mL each)
2 rubber stoppers (one with one hole, the second with two holes)
3 lengths of straight glass tubing (4cm, 8cm, and 10cm; should fit tightly into the stoppers)
15cm of rubber tubing (should fit tightly over the glass tubing)
150-200mL of cold (tap) water
1 balloon
Procedure
PREPARE THE STOPPERS:
In all cases, below, the glass tubing should fit snugly into the stoppers – it must form an airtight seal.
Insert the 4cm length of glass tubing (A) fully into the one-holed stopper so that it just reaches the bottom of the stopper, with about 2cm protruding from the top side of the stopper.
Insert the 10cm glass tube (B) into the two-holed stopper, so that approximately 2cm protrudes from the top of the stopper and about 6cm extends from the bottom of the stopper.
Insert the remaining, 8cm, glass tube (C) fully into the two-holed stopper, so that it just reaches the bottom of the stopper, with about 6cm protruding from the top side of the stopper.
Connect the glass tube (A) from the one-holed stopper to the top of the glass tube (B) that protrudes from the bottom of the second stopper using the rubber tubing. Ensure that the rubber tubing is about 1.5cm over the glass tubing on each side, and is not loose.
PREPARE THE FLASKS:
Fill one Erlenmeyer flask with about 100-125mL of concentrated sodium hydroxide solution
I normally prepare my own solution with enough solid sodium hydroxide to cover the base of the flask – the dissolution of sodium hydroxide is extremely exothermic – the flask will be very hot when done.
Fill the second flask with 150-200mL of cold water and firmly seal with the 2-holed stopper. The glass tube extending into the flask should be immersed in the water, but at least 1cm from the bottom. The other tube should not touch the water.
THE REACTION:
Note: the next steps must be done in quick succession – have all necessary materials within reach and be familiar with the steps before proceeding.
While there are many easy ways of generating small quantities of hydrogen gas (e.g. zinc in hydrochloric acid), filling a balloon requires two key aspects – firstly, a reasonably large quantity (several litres), and secondly a somewhat high pressure, which are not as commonly seen.
The procedure below involves mixing aluminum powder with a concentrated sodium hydroxide solution and bubbling the resulting gas through water to cool and purify, before capturing the gas in a balloon.
Safety Notes
Warning: this reaction, in the form presented below, is not exactly friendly – proceed at your own risk
Perform this reaction in a fume hood if possible
The initial reaction produces a minimum of fumes, but excess hydrogen may be vented; additionally, there is a risk of the (hot, caustic) reaction product spilling and the balloon bursting/exploding.
Ensure you use a Pyrex/Kimax flask
The reaction is highly exothermic and a regular glass flask will shatter at the peak of the reaction
Wear gloves
Part of this procedure requires holding the flasks during the reaction – you will be maintaining the seal manually and there is a high chance that you will get hot, concentrated sodium hydroxide on your hands.
Wear goggles (and possibly a lab coat)
This reaction has a risk of explosion, and uses extremely caustic chemicals that will reach very high temperatures during the reaction.
Avoid sources of static electricity (e.g. sweaters)
The balloon, once filled, can explode unexpectedly, especially if exposed to small electrical discharges.
Note: this is a violent reaction – it takes a moment to get going, but accelerates rapidly – the products are extremely hot. If necessary, you can slow the reaction down by immersing the reaction flask in a container of cold water for the duration of the reaction.
Materials
Note: quantities are approximate.
100-125mL of concentrated (~18M) sodium hydroxide solution
2mL of aluminum powder (about 2cm in a standard test tube)
2 Erlenmeyer flasks (250mL each)
2 rubber stoppers (one with one hole, the second with two holes)
3 lengths of straight glass tubing (4cm, 8cm, and 10cm; should fit tightly into the stoppers)
15cm of rubber tubing (should fit tightly over the glass tubing)
150-200mL of cold (tap) water
1 balloon
Procedure
PREPARE THE STOPPERS:
In all cases, below, the glass tubing should fit snugly into the stoppers – it must form an airtight seal.
Insert the 4cm length of glass tubing (A) fully into the one-holed stopper so that it just reaches the bottom of the stopper, with about 2cm protruding from the top side of the stopper.
Insert the 10cm glass tube (B) into the two-holed stopper, so that approximately 2cm protrudes from the top of the stopper and about 6cm extends from the bottom of the stopper.
Insert the remaining, 8cm, glass tube (C) fully into the two-holed stopper, so that it just reaches the bottom of the stopper, with about 6cm protruding from the top side of the stopper.
Connect the glass tube (A) from the one-holed stopper to the top of the glass tube (B) that protrudes from the bottom of the second stopper using the rubber tubing. Ensure that the rubber tubing is about 1.5cm over the glass tubing on each side, and is not loose.
PREPARE THE FLASKS:
Fill one Erlenmeyer flask with about 100-125mL of concentrated sodium hydroxide solution
I normally prepare my own solution with enough solid sodium hydroxide to cover the base of the flask – the dissolution of sodium hydroxide is extremely exothermic – the flask will be very hot when done.
Fill the second flask with 150-200mL of cold water and firmly seal with the 2-holed stopper. The glass tube extending into the flask should be immersed in the water, but at least 1cm from the bottom. The other tube should not touch the water.
THE REACTION:
Note: the next steps must be done in quick succession – have all necessary materials within reach and be familiar with the steps before proceeding.
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