Question

Someone knows how to solve this? It was found that 0.0005 mol of Ca (OH) 2 dissolved in 100 cm3 of solution is 80% dissociated. Calculate the pH of this solution.

Answer 1

pH = 11.9

Step-by-step explanation:

First, we determine the number of OH⁻ moles dissolved:

80% of Ca(OH)₂ is dissolved:

• 0.0005 mol * 80/100 = 4x10⁻⁴ mol Ca(OH)₂

There are two OH⁻ moles per Ca(OH)₂ mol:

• 4x10⁻⁴ * 2 = 8x10⁻⁴ mol OH⁻

Now we can calculate the molar concentration of OH⁻ (moles/L):

• 100 cm³ = 100 mL

• 100 mL ⇒ 100/1000 = 0.1 L

• [OH⁻] = 8x10⁻⁴ mol / 0.1 L = 8x10⁻³ M

Then we calculate the pOH of the solution:

• pOH = -log[OH⁻] = -log(8x10⁻³ M) = 2.10

Finally, we can calculate the pH of the solution using the equation

• pH + pOH = 14

• pH = 14 - pOH = 14 -2.10

• pH = 11.9