A solution of NaOH was prepared in a chemistry lab and the pOH was determined to be 9.3. What is the concentration of OH⁻ ions of this basic solution?

• A. 5 × 10⁻¹¹ M
• B. 5 × 10⁻¹⁰ M
• C. 2 × 10⁹ M
• D. 2 × 10⁸ M

Answer: (B)

Verified step by step guidance

1. Understand the nature of aqueous solutions: Aqueous solutions are those where water is the solvent. The pH scale is used to determine the acidity or basicity of a solution, with 7 being neutral, below 7 acidic, and above 7 basic.
2. Analyze the first statement: 'For a basic solution, the concentration of H3O+ is greater than the concentration of OH-.' In a basic solution, the concentration of OH- is actually greater than that of H3O+, so this statement is false.
3. Evaluate the second statement: 'The pH of a neutral aqueous solution is 7.00 at all temperatures.' This is incorrect because the pH of pure water is 7.00 only at 25°C. At other temperatures, the pH can vary slightly due to changes in the ionization of water.
4. Consider the third statement: 'An acidic solution under normal conditions has a pH value less than 7.00.' This statement is true, as acidic solutions have a higher concentration of H3O+ ions, resulting in a pH less than 7.
5. Examine the fourth statement: 'If the concentration of H3O+ decreases then the concentration of OH- will also decrease.' This is false because, according to the water ion product (Kw), if the concentration of H3O+ decreases, the concentration of OH- must increase to maintain the constant value of Kw at a given temperature.