The work of Dr. Mahmoud Marsafy

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REMEMBER: you must do your own experiment risk assessment, ideas are illustrated but health and safety details are NOT included

23. The pH of common liquid products

Comments on the Chart for measuring pH of common products with the Universal Indicator [UI]

The micro-scale technique presents several advantages for this type of experiments.  Instead of the usual test tubes, and beakers, and the conventional dropper bottle for the universal indicator, a multi-cavity plastic sheet and small plastic dropper bottles are utilized. Samples of the solutions to be investigated are transferred to their labeled dropper plastic bottles. The universal indicator solution is manipulated from a small plastic dropper bottle.

• In each of the cavities 10 drops of water are added followed by one drop of universal indicator. The colurs should be uniformly green in all the cavities utilized. Then one drop of each product is added to a different cavity and stirred with a micro-stirrer ( any thin small plastic rod will be suitable). The distinct colour change depending on the pH of the solution will be immediately revealed. The pH of the solution can then be deduced from the colour scale of the universal indicator utilized.

This technique is an excellent example of fair testing for comparison of the various pHs of the products. It is highly economical, and offers the opportunity of compactly organizing the laboratory activities when several products are to be investigated.

• Since the product solution is actually diluted 10 times then the colour of some of the products such as cola drinks will not mask their acidic indicator colours.

The recommended procedure above can of course be altered in many ways. But one should adhere to the preferred ratios of the drops of water, universal indicator and drops of the product solutions. The cavities in the plastic sheet utilized were only 0.5cm³ volume and the recommended number of drops was very easily and precisely transferred and conveniently contained within the cavities.

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