pH

Some chemicals are acids and they react with the water to make it acidic. The pH is the way in which we measure the acidity of the water. The pH scale goes from 1 to 14. A pH of 1 is very acidic and a pH of 14 means that not much acid is present at all. Some times we use chemicals called indicators that change colour at different pH levels. Universal indicator is one such chemical. Below are the colour ranges for the pH levels.

Colour changes of Universal indicator at differetn pH.

There is another group of chemicals called bases. These react with acids to neutralize them. At pH levels above 7 there is more base in the water than acid. At pH of 7 there is equal base and acid in the water and the water is said to be NEUTRAL.

Carbonated drinks have carbon dioxide gas dissolved in them. This gas makes the water very acidic. As the drink is left open carbon dioxide escapes and the drink becomes less acidic over time. Below is a graph of the pH of a particular brand of Soda Water at 25C.
At 10 am on Tuesday morning a wooden building, in an industrial estate, went up in flames. A person was arrested and questioned. "I was not around at 10 o'clock I was drinking alone at home." When the charred remains of the building cooled, forensic scientists moved in and collected evidence. At 6 pm they found a half full bottle of Soda Water near the gate of the complex with the suspects fingerprints. The sample of drink was tested with Universal Indicator. The result is shown on the left. An identical bottle was tested and its pH measured and shown on the graph above. Is the suspect telling the truth?
Explain.
Continue with "Acids-bases and conductivity"

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