Question

Why does a cake turn bitter and harder on adding baking soda in it?

Answer 1

First there is the taste. Baking soda is a base, and these have bitter tastes.

Secondly, it doesn't turn the food hard, rather it makes  it fluffy due to the release of CO2 when it reacts with the acid present in the powder before. The bubbles of CO2 make the food fluffy.

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