Acid–base reactions are hard to observe because they usually do not provide any visual cues. in this lab, you used a thermometer to determine that a reaction occurred between vinegar and sodium hydroxide. how could you detect the changes caused by this reaction in a classroom laboratory if you did not have access to a thermometer

Answer is: using acid-base indicator or pH indicators.

Acid-base indicators are usually weak acids or bases and they are chemical detectors for hydrogen or hydronium cations.
Example for acid-base indicator is phenolphthalein (molecular formula C₂₀H₁₄O₄). Phenolphthalein is colorless in acidic solutions and pink in basic solutions.
Another example is methyl orange. It is red colour in acidic solutions and yellow colour in basic solutions.

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one negative thing it that it can kill water animals. another negative thing is it can cause the destruction of ecosystem. one way water pollution can be reduced is to conserve energy.