Question

What concentration of sodium hydroxide is needed to give an aqueous solution with a pH of 12.790 ? Molarity of sodium hydroxide = M

Answer 1

To find the concentration of NaOH needed for a pH of 12.790, calculate the pOH by subtracting the pH from 14, then determine [OH-] with the antilog of the negative pOH. The resulting hydroxide ion concentration is equal to the molarity of NaOH.

Step-by-step explanation:

To calculate the concentration of sodium hydroxide (NaOH) needed to give an aqueous solution with a pH of 12.790, we must first understand the relationship between pH and pOH in the context of strong electrolytes.

Since NaOH is a strong base, it dissociates completely in water to form Na+ and OH- ions. To find the pH of the solution, we take into account the inverse logarithmic relationship between the hydroxide ion concentration ([OH-]) and pOH, given by the equation pOH = -log[OH-].

First, we calculate the pOH by subtracting the given pH from 14 (since pH + pOH = 14 for aqueous solutions). Thus, pOH = 14 - 12.790 = 1.210.

We then find the hydroxide ion concentration by taking the antilog (inverse logarithm) of the negative pOH: [OH-] = 10-pOH = 10-1.210. After finding the [OH-] concentration, this value will also be the molarity of NaOH (M) because one molecule of NaOH produces one OH- ion.

Answer 2

To achieve a pH of 12.790 with sodium hydroxide solution, a molarity of 0.0615 M NaOH is needed since it completely dissociates into Na+ and OH- ions in solution.

Step-by-step explanation:

To calculate the concentration of sodium hydroxide (NaOH) needed to achieve a pH of 12.790, we first need to convert the pH value to the concentration of hydroxide ions (OH¯). The pH scale is based on the concentration of hydrogen ions (H+), but for a base like sodium hydroxide, we are interested in the concentration of OH¯ ions. The pOH is calculated as 14 - pH, which gives us 14 - 12.790 = 1.210. The concentration of OH¯ ions is then found using the formula [OH¯] = 10¯(pOH), which yields 10¯(-1.210) = 0.0615 M. Because NaOH is a strong base that completely dissociates into Na+ and OH¯ ions, the molarity of NaOH needed to achieve this pH is also 0.0615 M.