Find the pH of a solution prepared by taking a 50.0 mL aliquot of a solution prepared by dissolving 12.25g of NaOH and 250.0 mL of water and diluting that aliquot to 1.00L?
12.25 g NaOH = ?? moles
moles = grams/molar mass = 12.25/40 = about 0.3 moles (you need to do it more accurately).
Place that in 250 mL and the molarity is
M = moles/L = 0.3/0.25 = about 1.2 M.
The concn of the diluted aliquot then is about 1.2 x (50/1000) = about 0.061
This is a solution of a strong base since NaOH ionizes 100%; therefore,
pOH = -log(OH^-) = -log(0.06) = about 1.2 and pH + pOH = 14. Solve for pH.
12.79
To find the pH of a solution, we need to determine the concentration of hydrogen ions (H+) in the solution. In this case, we can use the concentration of hydroxide ions (OH-) to calculate the concentration of hydrogen ions using the equation for water dissociation.
First, let's determine the concentration of the NaOH solution before dilution:
Concentration (mol/L) = Number of moles / Volume (L)
The number of moles of NaOH is given by its molar mass:
Molar mass of NaOH = 23.0 g/mol (Na) + 16.0 g/mol (O) + 1.0 g/mol (H)
= 40.0 g/mol
Number of moles of NaOH = Mass (g) / Molar mass (g/mol)
= 12.25 g / 40.0 g/mol
= 0.30625 mol
The volume of the NaOH solution is given as 250.0 mL, which needs to be converted to liters:
Volume (L) = 250.0 mL / 1000 mL/L
= 0.25 L
Now we can determine the concentration:
Concentration (mol/L) = 0.30625 mol / 0.25 L
= 1.225 mol/L
Since we diluted the solution by taking a 50.0 mL aliquot and making it a total volume of 1.00 L, the concentration of the diluted solution is 1/20 of the original concentration:
Diluted Concentration (mol/L) = 1.225 mol/L / 20
= 0.06125 mol/L
Next, we can calculate the concentration of the hydroxide ions (OH-) in the solution. Since NaOH is a strong base, it completely dissociates into Na+ and OH- ions:
Concentration of OH- (mol/L) = Diluted Concentration (mol/L)
= 0.06125 mol/L
Now, we can use the fact that water dissociates into equal amounts of H+ and OH- ions in pure water at 25°C:
[H+] = [OH-] = 10^-7 mol/L
Since the concentration of OH- ions is 0.06125 mol/L, we can subtract this value from the concentration of H+ ions:
[H+] = 10^-7 mol/L - 0.06125 mol/L
To find the pH, we take the negative logarithm (base 10) of the concentration of H+ ions:
pH = -log[H+]
Calculating the pH:
pH = -log(10^-7 mol/L - 0.06125 mol/L)
Now, we can substitute the value into a calculator or software to find the pH.