COLOURS OF pH INDICATORS

 CHEMISTRY BEHIND INDICATORS 

Mrs.Sulekha Rani.R , PGT Chemistry, KV NTPC kayamkulam 

pH scale actually is is a logarithmic scale for measuring the concentration of hydrogen ions in a solution. This means that, for every number you go down on the pH scale, the concentration of hydrogen ions increases by a factor of ten. The higher the concentration of hydrogen ions in a solution, the more acidic the solution is.

What does this have to do with the colour changes of indicator solutions? Well, the indicators themselves are actually either weak acids or bases. When they’re dissolved in water, their molecules dissociate slightly and form ions. Indicators tend to be molecules containing a fair number of alternating (conjugated) carbon-carbon double bonds and single bonds, such as phenolphthalein, shown below:

                                                               Phenolphthalein

These alternating double/single bonds can absorb wavelengths from visible light, making them appear coloured. In acidic solutions, the large number of hydrogen ions already in solution means that the molecule will not dissociate much, and so the colour seen will be that of the original indicator molecule. In basic solutions however, the comparative lack of hydrogen ions in solution leads to the molecule losing a hydrogen ion; this, put simply, changes the arrangement of electrons in the molecule, causing it to absorb different wavelengths of light and appear a different colour.

It’s not only set chemical indicators that can be used to indicate pH changes. Chemicals found naturally in various plants can also be used – for example, anthocyanin compounds in red cabbage

The Chemistry of the World Cup Football-2014 - BRAZUCA

The Chemistry of the World Cup Football-2014 - BRAZUCA  

Mrs . Sulekha Rani.R , PGT Chemistry, KV NTPC kayamkulam

 

A number of chemical materials are used in the manufacture of the Brazuca, the World Cup football. The majority of these materials are polymers; these are very long molecules built up from many smaller component molecules. A simple, everyday example is polyethene, used to make some plastic bags. Different classes of polymers are used to achieve particular properties for the ball.

Footballs consist of three main component parts: the covering (the outermost layer), the lining, and the bladder. Obviously, these will be designed in a manner that provides the most favourable aerodynamic properties for the ball – however, that’s veering dangerously into physics territory. None of these properties would be achievable without chemistry providing the materials required, so here’s a breakdown of the different types of polymers used in each component part of the ball.

Covering

The covering of the ball is made of six polyurethane panels, which are thermally bonded together. This covering is important to protect the ball, and to prevent it from absorbing too much water – the water absorption of the Brazuca ball is just 0.2%. This makes the ball much lighter than the leather-coated balls used in the past. Some balls may also have a polyurethane foam layer underneath the covering.

Polyurethanes are built up from compounds called isocyantes and polyols. The middle parts of these molecules can be varied to give different polyurethanes with differing properties. Polyurethanes have a wide range of applications, including foam in seating, adhesives, synthetic fibres and even skateboard wheels.

Cheaper footballs may use PVC (polyvinyl chloride) instead of polyurethane for the coating. They may also be stitched together, rather than thermally bonded. This stitching will be made from another class of polymers called polyesters; on higher end balls this stitching may be reinforced with Kevlar.

Lining

Underneath the covering layer, the ball will have several layers of lining. These are present to improve the bounce and strength of the ball. In the World Cup ball, these are made from another class of polymers, polyamides, more commonly referred to as nylon. Polyesters can also be utilised for this purpose. 

Nylon and polyesters are also commonly used components in the manufacture of football shirts, as well as other clothing. Nylon is additionally used in parachutes, ropes and fishing nets, whilst polyesters can be found in bed sheets, carpets and plastic bottles. 

Bladder

The bladder is the part of the football that holds the air. In the Brazuca, this is made from butyl rubber, but it can also be made from latex. Both have their benefits: butyl rubber retains the air for a longer period of time, whilst latex provides better surface tension. Butyl rubber can also be found in the valve through which air can be pumped into the ball, where it aids air retention. Silicone valves can also be used.

Most modern chewing gum also uses food grade butyl rubber to give the gum its elasticity. Unfortunately, it also contributes the unwanted stickiness of gum. It can also be found in the inner tubing of tyres.

This is just a peek into the world of polymers – any plastics you use on a day-to-day basis are composed from polymers, as well as your clothing, and many other everyday items. Without synthetic polymers, the World Cup would be kicking off today with a much more rudimentary ball!

Ref: Compound Interest