The pH of saturated Sr(OH)2 (aq) is found to be 13.12. A 10.0 mL sample of saturated Sr(OH)2 (aq) is diluted to 250.0 mL in a volumetric flask. A 10.0 mL sample of the diluted Sr(OH)2 (aq) is transferred to a beaker, and some water is added. The resulting solution requires 26.4 mL of a HCl solution for its titration.
What is the molarity of this HCl solution?
You know pH, I would convert to pOH, then to (OH^-). That will be (OH^-) = ?? moles/L of solution. You take 10.00 mL of that and dilute to 250 mL; therefore, the new (OH^-) = ?? moles/L x 10/250 = xx moles/L= xx M of the solution to be titrated.
Then titration is
mL acid x M acid = mL base x M base
Check my thinking. I did NOT correct for the 2OH^- in Sr(OH)2 since we always worked directly with pH, pOH, etc., and never converted to molarity Sr(OH)2
9.987*10^-4
To find the molarity of the HCl solution, we need to use the concept of stoichiometry and the volume of the HCl solution used during titration.
Here's how we can calculate the molarity of the HCl solution:
1. Determine the number of moles of Sr(OH)2 in the original 10.0 mL sample.
- Since Sr(OH)2 is a strong base, it dissociates completely in water.
- The molar mass of Sr(OH)2 is:
Sr: 87.62 g/mol
O: 15.999 g/mol (2 atoms)
H: 1.00784 g/mol (4 atoms)
- The molar mass of Sr(OH)2 is: (87.62 g/mol) + (15.999 g/mol * 2) + (1.00784 g/mol * 4) = 121.64 g/mol
- The mass of Sr(OH)2 in the 10.0 mL sample is: (10.0 mL / 1000 mL) * (13.12 g/L) = 0.1312 g
- The number of moles of Sr(OH)2 is: 0.1312 g / 121.64 g/mol = 0.00108 mol
2. Determine the number of moles of HCl used during titration.
- From the balanced chemical equation of the reaction between Sr(OH)2 and HCl:
2 HCl + Sr(OH)2 -> SrCl2 + 2 H2O
- The stoichiometry is 1:2 between HCl and Sr(OH)2.
- Therefore, the number of moles of HCl is twice the number of moles of Sr(OH)2: 0.00108 mol * 2 = 0.00216 mol
3. Determine the molarity of the HCl solution.
- The volume of the HCl solution used during titration is given as 26.4 mL.
- The number of moles can be calculated using the following formula:
Molarity = Moles / Volume (in liters)
- Convert the volume to liters: 26.4 mL / 1000 mL/L = 0.0264 L
- Calculate the molarity: Molarity = 0.00216 mol / 0.0264 L = 0.0818 M
Therefore, the molarity of the HCl solution is 0.0818 M.