Which of the following indicates a strong base is present?
A) pH close to 7 B) good conductor of electricity C) low reaction rate D) indicator turns green-blue
The Correct Answer and Explanation is:
The correct answer is B) good conductor of electricity.
Explanation:
A strong base is one that dissociates completely in water, releasing a large number of hydroxide ions (OH⁻). The presence of these free hydroxide ions in solution is what makes a substance a strong base. Let’s go over each option and explain why “good conductor of electricity” is the correct choice:
- A) pH close to 7: The pH scale ranges from 0 to 14, where a pH of 7 is considered neutral (neither acidic nor basic). Strong bases, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), typically have a pH above 7, often in the range of 12 to 14. Therefore, a strong base would not have a pH close to 7, which makes this option incorrect.
- B) good conductor of electricity: One of the key characteristics of strong bases is their ability to dissociate completely into ions when dissolved in water. This dissociation produces hydroxide ions (OH⁻) and cations (such as Na⁺ or K⁺), both of which are charged particles capable of carrying an electrical current. The presence of these ions in large quantities makes strong bases excellent conductors of electricity. For example, a 1 M solution of sodium hydroxide (NaOH) will readily conduct electricity due to the high concentration of ions. Therefore, this option correctly indicates the presence of a strong base.
- C) low reaction rate: Strong bases typically react quickly with acids and other substances. For example, a strong base like NaOH reacts immediately with acids to form water and salts in an exothermic reaction. Therefore, a “low reaction rate” would not be characteristic of a strong base, making this option incorrect.
- D) indicator turns green-blue: The color change of an indicator depends on the pH of the solution. For example, phenolphthalein turns pink in basic conditions. A green-blue color could be seen with certain indicators (like bromothymol blue) at a neutral to slightly basic pH, but it does not specifically indicate a strong base. Therefore, this option does not directly indicate the presence of a strong base.
In conclusion, the ability of a strong base to conduct electricity effectively due to the presence of free ions makes B) good conductor of electricity the correct answer.