Final answer:
When lime water and soda are mixed in the presence of an acid, carbon dioxide gas is produced, causing the limewater to turn milky. This indicates the presence of carbon dioxide.
Step-by-step explanation:
When you mix lime water and soda, specifically sodium bicarbonate or sodium carbonate with an acid like hydrochloric acid, an observation made is the formation of carbon dioxide gas. This gas then reacts with calcium hydroxide in the limewater to produce calcium carbonate, which is only slightly soluble in water. As a consequence, the limewater turns from clear to milky, indicating the presence of carbon dioxide gas.
Additionally, if vinegar and baking soda are mixed, the pH of the solution would change as the acidic vinegar reacts with the basic baking soda, releasing carbon dioxide and forming water and a salt.