Brainiac Alkali Metals

from scientist303




Alkali metals react with water reducing its protons to H2(g) and leaving an alkaline aqueous solution due to alkali metal hydroxide formation. When going down in the group from lithium to cesium the alkali metals give its electrons to the protons of water more easily and the reaction goes faster. As the reaction release heat, if this heat cannot be dissipated quickly enough the hydrogen released will get ignited, sometimes very violently, and react with atmospheric oxygen forming water again.

M(s) + H2O(l) = M(OH)(ac) + 1/2 H2(g) + lots of energy(*)!!...
H2(g) + ½ O2(g) + ignition energy(*) = H2O (g)!! + lots of energy!!...

SUGAR AND KClO3

from nuclearrabbit




Under thermal conditions or ignited by sulfuric acid, KClO3(s) decomposes to KCl(s) and 3/2 O2(g), which is a disproportionation reaction. The O2(g) generated oxidises very quickly carbohydrates as sucrose, C12H22O11(s,) liberating lots of heat, CO2(g) and H2O(g)...the presence of a bit of CuCl2(s) gives the bluish colour to the flames...very spectacular!!...

HYDROGEN AND CHLORINE

from chempics

H2 + Cl2 = 2 HCl

For the reaction to start an initiator is needed in order to overcome the activation energy. This can be a flame (as in this video) or just UV light...

VERY NICE LABCOAT by the way!!!

THE BARKING DOG REACTION

The Barking Dog demonstration is based on an exothermic reaction between nitrous oxide (N2O) or nitrogen monoxide (NO) and carbon disulfide (CS2). Ignition of the mixture in a long tube results in a bright blue chemiluminescent flash, accompanied by a characteristic barking or woofing sound. 
 What is happening in this demonstration is a redox reaction where the oxidant is the CS₂ and the reducing agent is the NO or N₂O. The reaction releases a lot of gas (N₂, CO₂, SO₂), which produces the woofing sound, elemental sulphur (S₈) which leaves a yellow layer covering all the tube inner part, and a lot of energy (bright blue chemiluminescent flash).

                        4 NO + CS₂ -> 2 N₂ + CO₂ + SO₂ + 1/8 S₈

THUNDER IN A TEST TUBE

HYPERGOLIC CHLORINATION OF ACETYLENE

Iron Wool Balance

from chempics

The reaction occurred is just the oxidation (redox reaction) of iron

4Fe + 3O2 = 2 Fe2O3 plus lots of energy

Iron need to be very fine divided (wool) to allow the combustion keep going (the activation energy burn iron is really high in comparison to other combustible materials as gasoline, wood or carbon) and as Fe2O3 is a solid (a normal burn, for instance of a piece of carbon, releases CO2 gas) the combustion result is heavier...

very nice experiment!!

COMPARING THE FOUR HALOGENS

from oulearn


Have a look especially to the reactions of bromine and iodine with aluminium...simply spectacular!!

FIREFLIES in a flask experiment

by basco36

Ammonium dichromate (NH₄)2Cr2O7 decomposes when heated yielding green chromium(III) oxide, nitrogen and water vapor. It is a comproportionation reaction where Cr(+6) of Cr2O7^2- gets reduced to Cr(+3) of Cr2O3 oxidising N(-3) of NH4⁺ to N(0) of N₂ gas. This process needs quite a lot of energy to get started and it can be used to simulate a chemical volcano. However, if hot (NH₄)2Cr2O7 is put in contact with NH₃(g) (ammonia), obtained from a saturated NH₄OH solution, the comproportionation is much faster as it can be seen on this video...

Underwater Fireworks: Sparklers

by thirstforscience

A sparkler (from wikipedia) is a type of hand-held firework that burns slowly while emitting colored flames, sparks, and other effects. They rely on REDOX reactions and therefore they contain two main components:

FUEL (reducing agent). There are two types:

• Metallic fuel, mandatory to make sparks; size of particles influences appearance of the sparks
• Aluminium or magnesium or magnalium, producing white sparks
• Iron, producing orange branching sparks
• Titanium, producing rich white sparks
• Ferrotitanium, for yellow-gold sparkles
• Additional fuel, optional, modifying the burning speed
• Sulfur
• Charcoal

OXIDIZER (oxidant agent). There are several types

• Potassium nitrate
• Barium nitrate
• Strontium nitrate
• Potassium perchlorate, more powerful but potentially explosive

As the sparklers contain their own oxidizer they don´t need to be in contact with air to burn out and therefore they work underwater!!

 

EXPLOSIVE copper oxide reduction with aluminium

from drgleisner 

Very nicely explained thermite type reaction where Al metal (aluminium 0) reduces CuO (copper +2) to form Cu metal (copper 0) and Al2O3 (Al +3) after some induction period on a Bunsen burner. Check out the reaction of the young audience!!

This is the redox process involved:

3 CuO  + 2 Al  = 3 Cu + Al2O3

Violent Hydrogen peroxide 85% decomposition

The decomposition of hydrogen peroxide consists formally in a redox reaction between two molecules of H₂O₂, one acting as a reducing agent and the other as oxidant. This is the overall reaction named disproportionation:

2 H₂O₂ = 2 H₂O + O₂(gas)

This decomposition is easier when concentrated H₂O₂ is used and can be catalysed by bases, light (hydrogen peroxide bottles are not transparent), or metals as it is shown on this video. In other words hydrogen peroxide can be considered as a reservoir of oxygen and this explains its oxidising properties.

COLOURFULL OXIDATION STATES OF VANADIUM

Sodium Vanadate (NaVO₃) is dissolved in diluted HCl giving a solution containing (VO₂)Cl through a dehydration (acid-base) reaction that also releases 2H₂O and NaCl (I made this up but I guess it is what actually happens):

NaVO₃ + 2 HCl = NaCl + H2O + (VO₂)Cl

(VO₂)Cl in solution gives YELLOW VO₂⁺ cations (Vanadium +5) which can be sequentially reduced (Zn-Hg amalgam) to BLUE VO²⁺ (Vanadium +4), to GREEN V⁺³ and finally to LAVANDER V⁺².