QuestionJune 3, 2025

81. What mass of KOH is necessary to prepare 800.0 mL of a so- lution having a pH=11.56 82. Calculate the concentration of an aqueous Sr(OH)_(2) that has pH=10.50

81. What mass of KOH is necessary to prepare 800.0 mL of a so- lution having a pH=11.56 82. Calculate the concentration of an aqueous Sr(OH)_(2) that has pH=10.50
81. What mass of KOH is necessary to prepare 800.0 mL of a so-
lution having a pH=11.56
82. Calculate the concentration of an aqueous Sr(OH)_(2) that has
pH=10.50

Solution
4.1(245 votes)

Answer

1. Determine the pOH from pH ### For KOH solution, pH + pOH = 14. Thus, pOH = 14 - 11.56 = 2.44. ## Step2: Calculate [OH⁻] concentration ### **[OH⁻] = 10^{-pOH}**. Therefore, [OH⁻] = 10^{-2.44} M. ## Step3: Calculate moles of KOH needed ### Volume in liters = 800.0 mL / 1000 = 0.8 L. Moles of KOH = [OH⁻] × Volume = 10^{-2.44} \times 0.8. ## Step4: Convert moles to mass ### Molar mass of KOH = 39.10 (K) + 16.00 (O) + 1.01 (H) = 56.11 g/mol. Mass = moles × molar mass. # Answer: ### Mass of KOH = 0.028 g # Explanation: ## Step1: Determine the pOH from pH ### For Sr(OH)_2, pH + pOH = 14. Thus, pOH = 14 - 10.50 = 3.50. ## Step2: Calculate [OH⁻] concentration ### **[OH⁻] = 10^{-pOH}**. Therefore, [OH⁻] = 10^{-3.50} M. ## Step3: Adjust for Sr(OH)_2 dissociation ### Sr(OH)_2 dissociates into 2 OH⁻ ions. So, [Sr(OH)₂] = [OH⁻]/2. # Answer: ### Concentration of Sr(OH)_2 = 3.16 × 10⁻⁴ M
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