Chemistry · 10

pH Scale and Indicators

The pH scale measures the acidity or alkalinity of a solution using the concentration of hydrogen ions (H+). pH indicators are substances that change

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Why is milk slightly acidic if no acid is added to it?

Milk contains lactic acid naturally, produced by bacteria during storage. Fresh milk is slightly acidic (pH ~6.6) due to dissolved CO2 and other weak acids, not from added acids.

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Can pH be negative or greater than 14?

Yes, pH can be negative for very strong acid solutions with [H+] > 1 mol/L. Similarly, pH can exceed 14 for very strong base solutions. However, the simple pH scale (0-14) applies to dilute solutions at 25°C.

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Why do we add indicators to acid-base titrations instead of using pH paper?

pH indicators show a sharp, distinct color change at the equivalence point, making it easy to detect when titration is complete. pH paper gives approximate values and is not precise enough for quantitative analysis.

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