Wednesday, January 28, 2009

The Manganese Rainbow

As you may well know, manganese salts are generally black or gray. At the first sight manganese salts do not appear to be very interesting. But at a closer look, this element won't appear so boring. Actually, I can easily say that this is one of my favourite elements for some of its particular reactions. Yesterday, while illustrating redox reactions, I had the opportunity to make one of manganese's most fascinating experiments.

The first two attempts went totally wrong, and when I was on the verge of succumbing my positive state and just give up, the farewell try went just marvelous. It's a very coloured experiment that you definitely shouldn't miss.

Glassware you need: one 100 ml cylinder; one 600 ml beaker; stirring rods; a burete.

Chemicals you need: 500 ml NaOH 6M; H2O2 0,1% (you can obtain it by dissolving 1 ml of pure H2O2 into 350 ml water); CH3COOH 6M; 0,05 g of KMnO4 dissolved in 1 ml of water and ice

How to do it: in the NaOH solution chilled at 0oC the entire quantity of permanganate is dissolved. Then from the burete 1 ml of H2O2 is added under continuous stirring. We can clearly observe now a palish green colour, because of the MnO42- ion. The reducing agent is H2O2.

2Mn7+O4-(aq) + 2HO-(aq) + H2O2 → 2Mn6+O42-(aq) + 2H2O + O2

You continue both adding H2O2 and stirring the upper layer of the substance until it gets cold blue.

2Mn6+O42-(aq) + 2HO-(aq) + H2O2 → 2Mn6+O43-(aq) + 2H2O + O2

On the top you should add now the CH3COOH, slowly and continuously stirring. Around 20 ml would be more than enough. A crimson red colour should be now observed due to the reaction between the hydronium and the trivalent permanganate ion previously formed.

In the end it should look like this:

Tips:

  1. Use only chilled NaOH
  2. Do not use indecorous proportions of the substances! Follow the gravimetric instructions as close as you can for an accurate result.
  3. When you mix, try to mix only the upper layer in order not to spoil the colours.
  4. Have fun doing this!

Tuesday, January 27, 2009

Persil, an inorganic detergent

Hi there again! I have indeed said that I will no longer post until the Chemistry Olympiad, but today while looking at a video about the chemical element Boron, I heard the fact that Persil is an inorganic detergent that has his name inspired from its two main compounds : sodium PERborate and sodium SILicate. So I did a little bit of research on the Internet and may I say that, I've found some pretty worth to mention things.
As I said earlier the two principal compounds of Persil are sodium perborate and sodium silicate. The major role of the perborate, in the washing process, is to decompose at high temperature in the washing machine in the presence of water to form hydrogen peroxide, and a B(OH)4- ion. In the next step, the hydrogen peroxide will remove the stains by oxidizing them and making them more soluble into the hot, boiling water.

A little bit of History Before the first world War, there were no detergents commercially available. Women had to wash clothes with house made soap in the water of the nearby river (only rich people could afford their water pumping system).

Image from http://www.hohenstein.de/en/index.asp

So, in 1907 Henkel started to commercialize the first detergent which was named after the two major components. This was to be one of the revolutionary inventions at the beginning of the XX-th century. But its great success wasn't felt immediately. Many people couldn't afford it, and it became popular only after the First World War, because it was widely used to wash the soldiers clothes. So only after that 4 years Henkel could lower the price in order to make it accessible to most of the people.

Original advertising poster

Nowadays, Persil is one of the very few toatally inorganic, commercially available washing products left on the market, that is widely used in Europe; the situation has pretty much changed in the last 100 years.

See you next time!

Tuesday, January 13, 2009

The Romanian National Chemistry Olympiad

Hi there again! Sorry for not writing for more than 2 weeks now, but I have been very busy with the chemistry Olympiad two Saturdays ago. I can say that I am very happy with my result, because I've managed at this point to qualify at the Romanian National Chemistry Olympiad, which takes place at Arad this year.

Because of the fact that the Olympiad is so close, and I have to learn a lot of new things in just 1 week, my chemistry teacher, Lidia Minza, gave me a few days off from school, in order to exercise some high-level problems, and to revise both theoretical and practical key aspects of Inorganic Chemistry, also mentioned in the Syllabus for the Olympiad.

So, see you after the Olympiad!

Saturday, January 3, 2009

ChimeXpert Contest, First Phase

Today I have seen the results for a chemistry contest I have participated in. The contest is called ChimeXpert and it is an international contest, organised by Romania (you can participate by registering at this link http://www.chimexpert.ro/index.php?id=29&L=2 and paying a fee of 12 Euro)

I've taken 247.5 points out of 300, which means that I correctly did 82.5% of the whole test. I was positioned first in my county, Galati, but I am pretty dissapointed because I have had higher self-expectations. Although my place in the county ranking may sound good, in the national classification I am only the 107th out of 282. In other words I am situated in the first 37.94%. I want to congratulate my classmate Andreea Stroia who obtained the same result as me.

The contest has taken place on-line, without a certain timebound and that means that participants could collaborate between them and even teachers could solve the problems for the participants. Even more, around 5% of the problems have been asked, in my and my teacher's opinion, wrongly (with none of the options correct - it is a 5 given options from which only one is correct test).

Now it is certain that I will pass to the next phase, but if I want to go to the international phase, I have to prepare myself a lot more because only the first 10% of all participants will pass.

With this post I invite anyone interested in Chemistry to participate in the following years, in order to make this contest truly international (I think many of my readers are high-school students or teachers).

Friday, January 2, 2009

New Year Chemistry

Happy New Year to All! I am going to talk in this post about Fireworks Chemistry, a very interesting subject may I say, with lots of Redox equations and thermal decompositions.

You surely have observed that fireworks are coloured in different ways: yellow, green, red, blue, purple, white and even more colours. A specific colour is produced when a metal or one of the metal's salts is burned into the air violently. In this way one metal or any of it's salts at the same oxidation state give the same colour which can be described as following, as a result of a very common flame test.

Element Flame Colour
Li+ Crimson red
Na+ Yellow
K+ Violet
Ca2+ Orange Red
Sr2+ Red
Ba2+ Dirty Yellow
B3- Green
Cu2+ Green

There are 2 characteristics of fireworks that are worth to be mentioned:

  1. Incandescence (light produced by heat)
  2. Substances like Magnesium (powerful white light) or Strontium (crimson red light) need a lot of heat in order to be put on fire. So a longer time is needed by these substances to catch fire. On the other way, there are substances like some Barium salts that are unstable even at room temperature. In order to synchronise the explosions of the substances with high igniting temperatures and of the substances with higher instability some metals like Aluminium, Magnesium or Titanium are added.

  3. Quality
  4. Sodium particles can contaminate fireworks so they will have a dirty yellowish shade. For this not to happen, MgO is added to the fireworks (it won't react unless there is some sodium). Also a very important aspect of fireworks' quality is the smoke: If too much is generated, the colours will be spoilt.

Generally, nitrate salts are used for fireworks, due to their instability, and light weight. For the igniting mechanism, phosphorus is preferred. Also, when we talk about fireworks there are two main igniting systems: in steps and all at once. Both need an initial explosive in order to make salts burn and after that shine is diverse colours. This substance is generally an ammonium salt due to it's instability and explosive properties.

A two step igniting system
Of course, what I presented is only a very vague description of the phenomena, because I didn't include reactions or more complex diagrams, in order just to create a general impression about the subject. I can only now wish you again a Happy New Year!