Final answer:
Vinegar, with a pH of 2.9, is an acidic substance due to its content of acetic acid. Sodium bicarbonate (baking soda) acts as a base when mixed with vinegar. The pH scale determines if substances are acidic, basic, or neutral; with values below 7 being acidic, 7 being neutral, and above 7 being basic.
Step-by-step explanation:
Vinegar has a pH of 2.9, indicating that it is an acidic substance. This low pH value means that vinegar contains a higher concentration of hydrogen ions (H+) than a neutral substance like pure water, which has a pH of 7. Vinegar is composed of acetic acid (ethanoic acid, CH3COOH), which is a weak acid, but still gives vinegar its acidic properties.
When vinegar is mixed with baking soda, a base, during the preparation of bread, the substance that serves as a base is the baking soda, or sodium bicarbonate (NaHCO3). A chemical reaction occurs between the acetic acid in vinegar and the baking soda, releasing carbon dioxide gas which helps the bread to rise.
To determine if a substance is acidic, basic, or neutral based on its pH, you can follow this general rule: Any substance with a pH less than 7 is considered acidic, a pH of exactly 7 is neutral, and a pH greater than 7 is basic. Applying this rule:
- Human blood, pH = 7.4, is slightly basic (alkaline).
- Household ammonia, pH = 11.0, is basic.
- Cherries, pH = 3.6, are acidic.