Acids, bases and salts - The characteristic properties of acids and bases (3)
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1.
Describe the characteristic properties of bases in terms of their reaction with acids. Include in your description the concept of pH and the role of conjugate acids and bases.
Bases react with acids in a process called neutralization. This reaction results in the formation of a salt and water. The pH of the solution changes as a result of this reaction. A base increases the pH of a solution, making it more alkaline.
The pH scale is a logarithmic scale used to indicate the acidity or basicity of a solution, ranging from 0 to 14. A pH of less than 7 indicates an acidic solution, 7 indicates a neutral solution, and a pH of greater than 7 indicates a basic solution. Bases have a pH greater than 7.
During neutralization, a base reacts with an acid to form a salt and water. The hydrogen ions (H+) from the acid react with the hydroxide ions (OH-) from the base to form water (H2O). The remaining ions form the salt. For example: HCl (acid) + NaOH (base) -> NaCl (salt) + H2O (water). The conjugate acid of a base is a weak acid, and the conjugate base of an acid is a weak base. The strength of a base is related to the strength of its conjugate acid; a strong base has a weak conjugate acid, and vice versa.
2.
The pH of a solution is 3. State what this pH value indicates about the concentration of H+ ions in the solution. Also, name a common alkaline substance and explain how it affects the concentration of OH- ions in water.
A pH of 3 indicates that the concentration of H+ ions in the solution is high. A pH scale of 0-14 is used to measure acidity and alkalinity. A pH less than 7 indicates an acidic solution, and a lower the number, the higher the concentration of H+ ions. Therefore, a pH of 3 indicates a relatively strong acid.
A common alkaline substance is sodium hydroxide (NaOH). Sodium hydroxide is a strong base and dissociates completely in water to produce sodium ions (Na+) and hydroxide ions (OH-). This dissociation increases the concentration of OH- ions in the water.
| Reaction | Equation |
| Dissociation of NaOH | NaOH(s) → Na+(aq) + OH-(aq) |
3.
Describe the neutralisation reaction between an acid and an alkali. In your description, include the reactants, products, and the ions involved in solution. Explain the process that occurs during the reaction.
The neutralisation reaction is a chemical reaction between an acid and an alkali. It results in the formation of a salt and water. The general equation for the reaction is: Acid + Alkali → Salt + Water. Specifically, the reaction between an acid and an alkali produces a salt and water, with the hydrogen ions (H+) from the acid reacting with the hydroxide ions (OH-) from the alkali to form water (H2O).
The process involves the proton transfer from the acid (H+) to the alkali (OH-). The hydrogen ion from the acid combines with the hydroxide ion from the alkali to form water. This process effectively removes the acidic and alkaline properties from the solution, resulting in a neutral solution. The salt formed is an ionic compound, and it remains dissolved in the water. The reaction is exothermic, meaning it releases heat.
Example: Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to produce sodium chloride (NaCl) and water.
Equation: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)