List two observations which you make when you add a pinch of sodium hydrogen carbonate to acetic acid in a test tube. Write chemical equation for the reaction that occurs.

When a pinch of sodium hydrogen carbonate ($NaHCO_3$) is added to acetic acid ($CH_3COOH$), the following observations are made:

1. Brisk effervescence is observed due to the rapid evolution of a gas.
2. A colorless and odorless gas (carbon dioxide, $CO_2$) is evolved, which turns lime water milky.

The chemical equation for the reaction is:

$$CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2$$