1. Fizzing and Gas Production: The most obvious sign is the fizzing or effervescence as carbon dioxide gas (CO₂) is released. This gas is produced from the reaction between the bicarbonate ion (HCO₃⁻) from baking soda and the hydrogen ions (H⁺) from citric acid.
2. Temperature Change: The reaction is slightly endothermic, meaning it absorbs a small amount of heat from the surroundings. You might notice a slight cooling effect as the reaction progresses.
3. Change in pH: Lemon juice is acidic, while baking soda is basic. The reaction produces salt (sodium citrate) and carbonic acid (H₂CO₃), which quickly decomposes into water and carbon dioxide. The overall effect is a decrease in pH, moving the solution towards being more neutral.
4. Taste Change: The mixture will lose the tartness of lemon juice and the slightly salty taste of baking soda. This is due to the formation of new compounds with different chemical properties.
The chemical equation for the reaction is:
NaHCO₃ (aq) + H⁺ (aq) → Na⁺ (aq) + H₂O (l) + CO₂ (g)
This equation only shows the reaction with hydrogen ions, but citric acid provides multiple H⁺ ions, leading to a more complex overall reaction.
In summary, the fizzing, gas production, slight temperature change, pH change, and taste change are all strong indicators that a chemical change has occurred when baking soda and lemon juice are mixed.
