Sodium dichromate

Dichromates are very useful salts used in organic oxidations. They're also used for the preparation of chromic acid which is legendary for its effectiveness at cleaning glassware. The main 3 dichromates used in labs are potassium dichromate, sodium dichromate and ammonium dichromate. Working with dichromates is not risk free as most of them are potent carcinogens.

This is how I make sodium dichromate:

I start with about 27g of chromium(iii) chloride, which I dissolve in some water to form a green solution. I then pour bleach into the chromium(iii) chloride solution until the colour changes from green to yellow. Bleach (sodium hypochlorite solution) is a very strong oxidizer and it oxidizes the green chromium(iii) chloride to yellow sodium chromate. Next I add a bit of hydrochloric acid to the yellow sodium chromate solution until it turns to orange sodium dichromate.

Chromates, dichromates and trichromates exist in equilibrium with each other. They can be converted to one another by adjusting the ph: chromates = basic neutral, dichromates = acidic and trichromates = very acidic.

Anyway, the orange sodium dichromate solution can be boiled down to yield the sodium dichromate in crystalline form. This is what mine looks like:

2 CrO4-2 + 2 H+ <===> Cr2O7-2 + H2O

Experimenting with potassium ferricyanide

Potassium ferricyanide, or potassium hexacyanoferrate, is an interesting salt used in cyanotype photography. It exists as deep red crystals, or as a yellow powder if finely ground. Despite the name it's pretty non-toxic and safe to work with. I acquired some recently and decided to try a few experiments with it.

I tried combining potassium ferricyanide with copper sulphate (both in solution) and immediately a dirty brown coloured precipitate of copper ferricyanide formed. The equation for this is:

2 K3Fe(CN)6 + 3 CuSO4 ==> Cu3(C6N6Fe)2 + 3 K2SO4

Another thing I tried was making Prussian blue, Fe7(CN)18. You may have heard of Prussian blue. It's a very common blue dye used in fabrics and painting. Its chemical name is ferric ferrocyanide, or ferrous ferricyanide. I made it by combining solutions of ferrous sulphate and potassium ferricyanide. The Prussian blue forms as a beautiful dark blue precipitate. Unfortunately I am unable to calculate the equation for this.

Here's some pictures of the products:










LEFT = copper ferricyanide
RIGHT = ferric ferrocyanide

Formic acid

Formic acid, or methanoic acid, is a carboxylic acid derived from methanol. Naturally it occurs in ant venom and various stinging nettles. It was first synthesized by French chemist Joseph Gay-Lussac using hydrogen cyanide. It's commonly prepared in the lab via the reaction of oxalic acid with glycerol. I used this method myself:


I started with 30ml of glycerol in a beaker. Under the beaker I placed a hotplate, which I turned to high heat to drive off all the water. It's important that water is kept to a minimum as it will lower the quality of the final product. Anyway, to the glycerol I added 24g of hydrated oxalic acid. I set up for simple distillation and heated the mixture untill it turned dark red. The formic acid distillate collected was placed in a vial for storage. This method produced very concentrated acid. It probably could have been even more concentrated if anhydrous oxalic acid had been used. The reaction can also produce allyl alcohol under certain conditions.

C2H2O4 ==> CH2O2 + CO2

Sodium bisulphite

Sodium bisulphite (NaHSO3) is an interesting compound with many uses. Upon contact with many strong acids, it reacts to form sulphur dioxide gas. Sodium bisulphite also forms adducts with many aldehydes. It's also a food additive (E222). My use for it, however, is to prepare sodium hydroxyethylsulphonate.

Making sodium bisulphite is fairly simple. I had a go at it.

I started by preparing a dilute solution of sodium hydroxide in water. I then set up a sulphur dioxide generator using burning sulphur. Burning sulphur produces very dirty impure sulphur dioxide but it's good enough for this purpose. Anyway, I bubbled sulphur dioxide through the sodium hydroxide solution for 1 hour. After this, the solution had turned quite yellow, and I began boiling it down until I saw a few crystals precipitating. At this point I stopped boiling down the solution and filtered out the crystals. These are sodium metabisulphite. I then transferred the filtrate to a beaker in an icebath and left it there for 1 hour. After this, a huge mass of crystalline sodium bisulphite had precipitated.

The crystals were collected via filtration and are shown here:

NaOH + SO2 ==> NaHSO3    NaHSO3 + NaOH ==> Na2SO3 + H2O

Methyl ethyl ketone peroxide

Methyl ethyl ketone peroxide (MEKP), or 2-butanone peroxide, is an organic peroxide with explosive properties. It exist in three forms: monomeric, dimeric and trimeric, dimeric being the most powerful explosive (and least shock sensitive) of the three. Its main use is as a catalyst for crosslinking specific polymers. Unlike its cousin acetone peroxide, MEKP is a liquid not a solid. It's also a lot safer than acetone peroxide and a lot less shock-sensitive.

I made some dimeric MEKP a few days ago DO NOT TRY THIS YOURSELF

I started by adding 25ml of methyl ethyl ketone to a 100ml beaker. I then poured in 30ml of 30% hydrogen peroxide. I placed the beaker of hydrogen peroxide/methyl ethyl ketone into an icebath. I left it in the icebath for 10 mins then poured in 15ml of concentrated (12M) hydrochloric acid (this serves as the catalyst). After the acid addition, the reaction mixture turned quite cloudy, due to suspended droplets of product. The mixture was left to stand overnight in the icebath. In the morning the mixture had separated into two layers (MEKP being the top layer). This mixture was poured into a 1L beaker containing 200ml of saturated sodium bicarbonate solution and vigorously stirred for 3 minutes. The mixture was then left to stand for 2 mins.

During this time, droplets of  MEKP were observed collecting and clumping together on the bottom of the flask. These liquid clumps of MEKP were extracted using a syringe and placed in a petri dish to dry.

After this I was left with fairly anhydrous dimeric MEKP (with some monomeric contamination).
I tried a few detonations with it as well. Here's some images:


                                            









left = anhydrous MEKP & right = MEKP deflagration

2 C4H8O + 2 H2O2 ===HCl==> C8H16O4 + 2 H2O

Glacial acetic acid

Acetic acid or ethanoic acid is a useful compound with many applications in the home lab. Glacial acetic acid is the name given to 100% anhydrous (water free) acetic acid, this is not the same thing as white vinegar which is 5% acetic acid.  I had a go at making some good glacial stuff a while ago:

I started by pouring around 90g sodium bisulphate into a round bottom flask. I then poured about half its volume of anhydrous sodium acetate into the flask. (The molar ratios aren't really important as the sodium bisulphate should be in excess). Next I attached an adaptor to the flask and a condenser and set up for simple distillation.

At around 60 C the sodium bisulphate began to melt and react. At about 90 C acetic acid was observed refluxing in the flask. At 100-110 C the acetic acid began to distil over and was collected. Once the acetic acid stopped coming over the distillation was stopped.

The distillate collecting had an extremely strong vinegary smell. I poured a small amount of the product into a test tube and added a bit of sodium bicarbonate. Very little reaction was observed showing that the acid was close to glacial. Dilute acetic acid reacts much more violently with sodium bicarbonate than glacial acetic acid does. This was the result of my work:

NaHSO4 + NaCH3COO ==> CH3COOH + Na2SO4

The sodium acetate and sodium bisulphate were very poorly mixed and ground up. This is probably why my yield was so low. Next time I try this I'll make sure they're ground and mixed together thoroughly.

Copper hydroxide and schweizer's reagent

This is one of the first experiments I ever performed. If aqueous ammonia is added to a solution of copper sulphate a light blue precipitate of copper hydroxide is formed. If  more ammonia is added the precipitate redissolves yielding a dark blue solution of tetraamminediaquacopper(ii) dihydroxide.

This is what happens:
The ammonia reacts with the water in a reversible reaction to form hydroxide ions and ammonium ions
NH3 + H2O <==> NH4+ + OH-

and the Copper sulphate dissolves in water to give hexaaquacopper(ii) ions and sulphate ions
CuSO4.5H2O + H2O ==> [Cu(H2O)6] (2+) + SO4 (2-)

The hydroxide ions and hexaaquacopper(ii) ions combine to produce copper hydroxide which precipitates
[Cu(H2O)6] 2+ + 2OH- ==> Cu(OH)2.2H2O + 4H2O

If more ammonia is added, schweizer's reagent (tetraamminediaquacopper(ii) dihydroxide) is formed
Cu(OH)2.2H2O + 4NH3 ==> [Cu(NH3)4(H2O)2](OH)2

[Cu(H2O)6] +2 + 4NH3 + 2 OH- ==> [Cu(NH3)4(H2O)2](OH)2 + 4 H2O

Tetraamminediaquacopper(ii) dihydroxide is an interesting compound. Its capable of dissolving cellulose. It cannot exist in its pure state and is only stable in aqueous solution or under a stream of ammonia. I don't really have any use for it or copper hydroxide, although it is interesting dissolving cotton with schweizer's reagent. Here's some pictures:


From left to right: copper hydroxide, schweizer's reagent.

Sodium copper dichloroisocyanurate

sodium copper dichloroisocyanurate is an exotic complex with the formula Na2[Cu(C3N3O3Cl2)4]. It exists as a purple powdery solid. If you own a fountain with copper in it, you my have come across this compound before. If you use sodium dichloroisocyanurate to treat your fountain water, it will slowly react with the copper generating some of this colourful complex. this will give the copper a light purple coating.

To make the complex I started with two beakers. In one I prepared a solution of copper sulphate and in the second, a solution of sodium dichloroisocyanurate. I combined the solutions slowly and as I did so a purple precipitate of sodium copper dichloroisocyanurate formed. I filtered the precipitate and dried it. Here's the slightly wet product:

CuSO4 + 4 Na(C3N3O3Cl2) ==> Na2[Cu(C3N3O3Cl2)4] + Na2SO4

I find using concentrated solutions of sodium dichloroisocyanurate and copper sulphate works best. If dilute solutions are used, the product takes a while to form and precipitate.