F.2 SCIENCE題,考試用

Hi,


Question :

Can the universal indicator measures coloured substance e.g black colour?will the result be affected ?



Answer :

The universal indicator is good for testing light - coloured material ,(e.g. calcium hydroxide , vinegar , lemon juice ,etc.)

But , it is not good for measuring coloured substance that is dark in colour ,(e.g.soy sauce, cocca cola , black beer , etc.)

It is because universal indicator is typically composed of water, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt. You can also see that the colour of this indicator itself is quite light , if the indicator is drop into those dark - coloured solution , the colour change of the tested material is not easy to observe by naked eye . In fact , it (the colour change of the tested material) can not be observed accurately by computer , either .

So, you have to make use of pH sensor , which is connected to a datalogger ,
and which the message produced by the datalogger is transmitted to a computer , and finally , under the computer ' s accuracy calculation, the pH value is formed on the screen of the computer monitor .

No pH paper please. Color of solution will also mask the color of the pH paper.

All acid-base indicators which show the results with colour changes are not suitable to measure the pH of samples with dark colours

The dark colours will mask the colour change, which leads to difficulty in indentifying the true result.

A pH meter will be more appropriate to measure the pH value of samples with dark colours.

of course not = =
results will definitely be affected

(for measuring pH value of coloured solution,
pH metre and pH paper are recommended.)