A saturated aqueous solution of calcium hydroxide, Ca(OH)2, is approximately 0.13% calcium hydroxide, by mass, and has a density of 1.02 g/mL. What is the pH of such a solution?
To determine the pH of the solution, we first need to find the concentration of hydroxide ions (OH-) in the solution. Since calcium hydroxide (Ca(OH)2) is a strong base, it dissociates completely in water to release two hydroxide ions for every one calcium hydroxide molecule.
Step 1: Calculate the mass of calcium hydroxide in the solution.
Given that the solution is approximately 0.13% calcium hydroxide by mass and has a density of 1.02 g/mL, we can calculate the mass of calcium hydroxide present in 1 mL of solution:
Mass of calcium hydroxide = 0.13% × 1.02 g = 0.00133 g
Step 2: Calculate the concentration of calcium hydroxide in the solution.
Since density is given in grams per milliliter (g/mL), the concentration can be expressed as grams per liter (g/L). We convert 0.00133 g to g/L by multiplying by 1000 (1 mL = 0.001 L):
Concentration of calcium hydroxide = (0.00133 g / 1 mL) × 1000 mL/L = 1.33 g/L
Step 3: Calculate the concentration of hydroxide ions (OH-) in the solution.
Since calcium hydroxide dissociates completely to produce two hydroxide ions for every one calcium hydroxide molecule, the concentration of hydroxide ions is twice the concentration of calcium hydroxide:
Concentration of hydroxide ions = 2 × 1.33 g/L = 2.66 g/L
Step 4: Convert the concentration of hydroxide ions to molarity.
To calculate the pH, we need the molar concentration of hydroxide ions. The molar mass of hydroxide (OH-) is 17.01 g/mol. We divide the concentration in g/L by the molar mass to get the molar concentration in mol/L:
Molar concentration of hydroxide ions = (2.66 g/L) / 17.01 g/mol = 0.156 M
Step 5: Calculate the pOH.
The pOH is the negative logarithm (base 10) of the hydroxide ion concentration:
pOH = -log10(0.156) ≈ 0.81
Step 6: Calculate the pH.
The pH is related to the pOH by the equation: pH + pOH = 14. Therefore, to find the pH, subtract the pOH from 14:
pH = 14 - 0.81 ≈ 13.19
Therefore, the pH of the saturated aqueous solution of calcium hydroxide is approximately 13.19.
To find the pH of a saturated aqueous solution of calcium hydroxide, we first need to calculate the concentration of hydroxide ions (OH-) in the solution.
Step 1: Calculate the molar mass of Ca(OH)2.
Calcium (Ca) has a molar mass of 40.08 g/mol, and each hydroxide (OH-) group has a molar mass of 17.01 g/mol.
Therefore, the molar mass of Ca(OH)2 is:
40.08 g/mol + 2 * 17.01 g/mol = 74.10 g/mol.
Step 2: Calculate the mass of calcium hydroxide in the solution.
The solution is approximately 0.13% calcium hydroxide by mass, which means 0.13 g calcium hydroxide is present in 100g of solution.
To convert this to grams per milliliter (g/mL), we can assume 100g of solution is equivalent to 100mL of solution (since the density is 1.02 g/mL).
Therefore, the mass of calcium hydroxide in 1 mL of solution is:
0.13 g / 100 mL = 0.0013 g/mL.
Step 3: Calculate the molar concentration of calcium hydroxide in the solution.
Molar concentration (Molarity, M) is calculated by dividing the moles of solute by the volume of the solution in liters.
First, we need to convert the mass of calcium hydroxide in 1 mL to moles.
Using the molar mass calculated in Step 1:
0.0013 g / 74.10 g/mol = 1.754 x 10^-5 mol/mL.
Since the density of the solution is 1.02 g/mL, we can convert the molar concentration to mol/L (M) using the density:
1.754 x 10^-5 mol/mL * 1.02 mL/g = 1.787 x 10^-5 mol/L.
Step 4: Calculate the concentration of hydroxide ions (OH-) in the solution.
Calcium hydroxide dissociates in water to form one calcium ion (Ca2+) and two hydroxide ions (OH-).
Therefore, the concentration of OH- ions is twice the concentration of calcium hydroxide:
2 * 1.787 x 10^-5 mol/L = 3.574 x 10^-5 mol/L.
Step 5: Calculate the pOH of the solution.
pOH is the negative logarithm (base 10) of the hydroxide ion concentration:
pOH = -log10(3.574 x 10^-5) = 4.447.
Step 6: Calculate the pH of the solution.
The pH is the negative logarithm (base 10) of the hydrogen ion concentration (H+). In a basic solution, the concentration of H+ is equal to 1 x 10^(-14) divided by the concentration of OH-:
pH = 14 - pOH = 14 - 4.447 = 9.553.
So, the pH of the saturated aqueous solution of calcium hydroxide is approximately 9.553.
1000 mL x 1.02 g/mL x 0.0013 = approx 1.4 grams Ca(OH)2 but that's just a close estimate.
Then mols = grams/molar mass Ca(OH)2 and since that is mols/L that is the M and = approx 0.02. Again, that's an estimate.
.......Ca(OH)2 ==> Ca^2+ + 2OH^-
I......0.02.........0.......0
C.....=0.02........0.02...0.04
E........0.........0.01...0.04
So pOH = -log(OH^-) and convert to pH with
pH + pOH = pKw = 14.
You know pKw and pOH, solve for pH.