Which of the following is a characteristic property of acids?

Analysis

The question asks for a characteristic property of acids. To solve this, we need to recall the fundamental chemical properties that define acids in an aqueous solution.

Concept Explanation

Acids are substances that, when dissolved in water, produce hydrogen ions ($H^+$). Their common characteristics include:

1. Taste: They have a sour taste (e.g., citric acid in lemons).
2. Litmus Test: They turn blue litmus paper red.
3. pH Scale: They have a pH value of less than 7.
4. Reactivity: They react with reactive metals (like Zinc, Magnesium, or Iron) to produce a salt and hydrogen gas.
5. Neutralization: They react with bases to form salt and water.

Step-by-Step Evaluation

• Option A: Incorrect. Acids turn blue litmus paper red. Turning litmus paper blue is a property of bases (alkalis).
• Option B: Incorrect. A bitter taste is a characteristic property of bases.
• Option C: Incorrect. A pH value above 7 indicates a basic (alkaline) solution. Acids have a pH below 7.
• Option D: Correct. When an acid reacts with a metal (e.g., $Zn + 2HCl \rightarrow ZnCl_2 + H_2$), hydrogen gas is evolved. This is a classic chemical test for acids.

Conclusion

Based on the chemical properties of acids, the correct characteristic is their ability to react with metals to produce hydrogen gas.

Exam Tip

Remember the acronym "BAR": Bases turn litmus Alkaline (blue) and Red litmus turns blue. For acids, just remember they are the opposite: they turn blue litmus red and have a pH < 7. Also, always associate "Acids + Metals" with "Hydrogen gas" as it is a very common JAMB question!