A 20.0 mL sample of 0.687 M HBr is titrated with a 0.216 M NaOH solution. The pH after the addition of 10.0 mL of NaOH is __________.
initial mols HBr = M x L = about 0.014
mols NaOH added = about 0.002
but you need to do them more accurately.
........NaOH + HBr ==> NaBr + H2O
I.........0....0.014....0.......0
added....0.002.....................
C.......-0.002..-0.002..0.002..0.002
E.........0.....0.0120...0.002.0.002
So what you have at 10.0 mL is a solution of HBr which is a strong acid (100% ionized); therefore, (H^+) = (HBr) so pH = -log(HBr)
Note: (HBr) = mols/L = 0.012/(0.010+0.020) = ?
Thank you so much that cleared up a lot!
To find the pH after the addition of the NaOH solution, we first need to determine the moles of HBr in the initial solution and the moles of NaOH that react with the HBr.
Step 1: Calculate the moles of HBr.
Moles of HBr = concentration × volume
= 0.687 M × 0.0200 L
= 0.0137 moles
Step 2: Calculate the moles of NaOH reacting with HBr.
Since the balanced chemical equation between HBr and NaOH is:
HBr + NaOH → NaBr + H2O
From the equation, we can see that the mole ratio between HBr and NaOH is 1:1.
Therefore, moles of NaOH reacting with HBr = 0.0137 moles
Step 3: Calculate the remaining moles of NaOH.
The volume of NaOH solution added is 10.0 mL, which is equal to 0.0100 L.
Moles of NaOH = concentration × volume
= 0.216 M × 0.0100 L
= 0.00216 moles
Step 4: Calculate the moles of the excess NaOH.
Moles of the excess NaOH = moles of NaOH added - moles of NaOH reacting with HBr
= 0.00216 moles - 0.0137 moles
= -0.0115 moles (negative because it's in excess)
Note: The negative value indicates that there is an excess of NaOH, which means that the reaction is complete and all HBr has been neutralized.
Step 5: Calculate the concentration of the remaining NaOH.
Concentration of NaOH = remaining moles of NaOH / volume
= (-0.0115 moles) / (0.0200 L + 0.0100 L)
= -0.460 M (Once again, the negative denotes the excess amount)
Step 6: Calculate the pOH of the solution.
pOH = -log[OH-]
= -log(0.460 M)
Step 7: Calculate the pH of the solution.
pH + pOH = 14 (at 25°C)
pH = 14 - pOH
By following these steps, you can obtain the pH after the addition of 10.0 mL of NaOH.