A student added solid K2O to a 750.0 mL volumetric flask. The solid was dissolved in water and then the flask filled with water to the mark. This formed 750.0 mL of the initial KOH solution. 20.0 mL of the initial solution was transferred to another flask and diluted to 200.0 mL. The pH of the diluted solution was 14.22.
a) What is the concentration of hydroxide ion is the diluted solution?
I found this to be 1.66M becaue PH + POH =14 so POH=-.22 then since pOH=-log(OH-) concentration of hydroxide ions would be 1.66M
(b) What is the concentration of hydroxide ion in the original solution?
M
(c) What mass of K2O was added to the first flask?
Yes
To find the concentration of hydroxide ions in the diluted solution, you correctly used the formula: pH + pOH = 14. Since the pH of the diluted solution is 14.22, we can find the pOH by subtracting the pH from 14.22:
pOH = 14 - 14.22 = -0.22
Since pOH = -log(OH-), we can rearrange the equation to find the concentration of hydroxide ions (OH-):
[OH-] = 10^(-pOH)
Plugging in the value of pOH, we get:
[OH-] = 10^(-(-0.22)) = 10^0.22 ≈ 1.66 M
Therefore, the concentration of hydroxide ions in the diluted solution is approximately 1.66 M.
To find the concentration of hydroxide ions in the original solution (before dilution), we can use the concept of dilution. Since 20.0 mL of the initial solution was transferred to another flask and diluted to 200.0 mL, we can set up the following equation using the dilution formula:
C1V1 = C2V2
where C1 is the initial concentration, V1 is the initial volume, C2 is the final concentration, and V2 is the final volume.
Plugging in the given values, we have:
C1 * 20.0 mL = 1.66 M * 200.0 mL
Solving for C1, we get:
C1 = (1.66 M * 200.0 mL) / 20.0 mL ≈ 16.6 M
Therefore, the concentration of hydroxide ions in the original solution (before dilution) is approximately 16.6 M.
To find the mass of K2O added to the first flask, we need to convert the volume of the initial solution (750.0 mL) to the moles of K2O.
We know that 1 mole of K2O corresponds to 2 moles of KOH since each K2O molecule provides 2 moles of hydroxide ions to the solution. Additionally, we can calculate the molar mass of K2O:
K: atomic mass = 39.10 g/mol
O: atomic mass = 16.00 g/mol
Molar mass of K2O = (2 * K atomic mass) + (1 * O atomic mass) = (2 * 39.10 g/mol) + (1 * 16.00 g/mol) = 94.20 g/mol
Now we can calculate the moles of K2O using the volume and concentration of the initial solution:
moles of K2O = (750.0 mL / 1000 mL/L) * (16.6 mol/L)
Finally, we can find the mass of K2O using its molar mass and the moles calculated above:
mass of K2O = moles of K2O * molar mass of K2O
The weight of K2O added to the first flask can be calculated using these steps.