How Do Acids, Bases, and Salts Impact Our Daily Lives?
FAQs on Acids, Bases, and Salts: Definitions, Properties & Uses
1. What is an acid according to the Arrhenius theory?
An acid is a substance that increases the concentration of hydrogen ions (H+) when dissolved in an aqueous solution. According to the Arrhenius theory, this dissociation into H+ ions is what gives acids their characteristic properties, such as a sour taste, the ability to turn blue litmus paper red, and to conduct electricity in solution.
2. What defines a substance as a base, and how does it differ from an alkali?
A base is a chemical substance that can neutralise an acid, typically by producing hydroxide ions (OH-) in a solution or by accepting H+ ions. The key difference lies in solubility: an alkali is a specific type of base that is soluble in water. Therefore, all alkalis are bases, but not all bases are alkalis. For example, sodium hydroxide (NaOH) is an alkali because it dissolves in water, while copper(II) oxide (CuO) is a base but is insoluble in water.
3. How is a salt formed and what are its components?
A salt is an ionic compound formed from the neutralisation reaction between an acid and a base. It consists of two parts: a cation (a positive ion) from the base and an anion (a negative ion) from the acid. For instance, in the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH), the Na+ from the base and the Cl- from the acid combine to form the salt sodium chloride (NaCl).
4. What are some common examples of acids and bases found in everyday life?
Many common household items are acids or bases.
- Acids: Common examples include acetic acid (found in vinegar), citric acid (in fruits like lemons and oranges), and carbonic acid (in carbonated drinks).
- Bases: Examples include sodium bicarbonate (baking soda), magnesium hydroxide (in antacids), and ammonia (in many household cleaning products).
5. How does the pH scale help in classifying the strength of acids and bases?
The pH scale is a logarithmic scale from 0 to 14 that measures how acidic or basic a substance is. A substance with a pH of 7 is neutral. A pH value below 7 indicates acidity, and the further the value is from 7, the stronger the acid (e.g., pH 1 is a very strong acid). A pH value above 7 indicates alkalinity, and the further the value is from 7, the stronger the base (e.g., pH 14 is a very strong base).
6. What is the difference between a strong acid and a concentrated acid?
These terms describe two different properties. Strength refers to the degree an acid ionises in water. A strong acid, like HCl, completely dissociates into its ions. A weak acid, like acetic acid, only partially dissociates. In contrast, concentration refers to the amount of acid dissolved in a given volume of water. It is possible to have a dilute solution of a strong acid or a concentrated solution of a weak acid.
7. Why is pH balance important in the human digestive system?
The pH level is critical for digestion. The stomach secretes hydrochloric acid, creating a highly acidic environment (pH 1.5-3.5). This low pH serves two main purposes: it kills most harmful microorganisms in food and activates the enzyme pepsin, which is essential for digesting proteins. After leaving the stomach, the food enters the small intestine, where the pH becomes alkaline to neutralise the stomach acid and allow different enzymes to work effectively.
8. What happens at a molecular level during a neutralisation reaction and what are its applications?
During a neutralisation reaction, the hydrogen ions (H+) from an acid react with the hydroxide ions (OH-) from a base. This combination forms a molecule of water (H₂O), which is a neutral substance. The remaining cation from the base and anion from the acid combine to form a salt. This principle has many applications, such as using antacids (bases) to neutralise excess stomach acid and treating acidic soil with lime (a base) to improve crop growth.
9. How are salts classified as acidic, basic, or neutral?
The type of salt depends on the strength of the acid and base that reacted to form it:
- Neutral Salts: Formed from a strong acid and a strong base (e.g., NaCl). Their aqueous solution has a pH of approximately 7.
- Acidic Salts: Formed from a strong acid and a weak base (e.g., NH₄Cl). They hydrolyse in water to produce an acidic solution with a pH less than 7.
- Basic Salts: Formed from a weak acid and a strong base (e.g., CH₃COONa). They hydrolyse in water to produce a basic solution with a pH greater than 7.
