20ml sample of .200M HBr is titrated w/ .200M NaOH. what is the ph after adding 15ml (base)?
HBr + NaOH ==> NaBr + HOH
Calculate mols HBr.
mols HBr = M x L = ??
Calculate mols NaOH used = M x L.
Subtract mols of one from mol of the other. The one in excess will give you the H^+ if it is HBr or OH^- if it is NaOH.
Then pH = -log(H^+) OR
pOH = -log(OH^-)
To find the pH after adding 15 ml of a base to a 20 ml sample of a HBr solution, we need to determine the moles of HBr and NaOH initially present, and then calculate the concentration of H+ ions in solution, which will give us the pH.
Step 1: Determine moles of HBr and NaOH initially present
Moles of HBr = concentration of HBr x volume of HBr solution
= 0.200 M x 0.020 L
= 0.004 moles
Moles of NaOH = concentration of NaOH x volume of NaOH solution added
= 0.200 M x 0.015 L
= 0.003 moles
Step 2: Determine the limiting reactant
The stoichiometric ratio between HBr and NaOH is 1:1, so whichever reactant is present in the lesser amount will be the limiting reactant. In this case, NaOH is the limiting reactant since it is present in a lesser amount.
Step 3: Calculate the moles of excess NaOH
Moles of excess NaOH = moles of NaOH initially present - moles of HBr reacted
= 0.003 moles - 0.003 moles
= 0 moles
Step 4: Calculate the moles of HBr reacted
Since NaOH is the limiting reactant, the number of moles of HBr reacted will be equal to the number of moles of NaOH.
Moles of HBr reacted = 0.003 moles
Step 5: Calculate the volume of HBr solution left after reaction
Volume of HBr solution left = initial volume of HBr solution - volume of NaOH added
= 0.020 L - 0.015 L
= 0.005 L
Step 6: Calculate the concentration of H+ ions
Concentration of H+ ions = moles of HBr reacted / volume of HBr solution left
= 0.003 moles / 0.005 L
= 0.6 M
Step 7: Calculate the pH
pH = -log10(H+ concentration)
= -log10(0.6)
≈ 0.22
Therefore, the pH after adding 15 ml of NaOH is approximately 0.22.