what volume of 0.0100 M NaOH must be added to 1.00 L of 0.0500 M HOCl to acheive a PH of 8.00?
Ka=3.5X10^-8
pH+pOH=14
14-8.00=pOH
pOH=-log[OH-], so [OH-]=10^(-6.00)=1x10^-6
HOCl + OH--------H20 + OCl-
.05M X 0
-X -X +X
.05-X 0 X
THEN USE HENDERSON-HASSELBACK EQUATION
pH=pKa+LOG[A-/HA]
8.00=-LOG(3.5X^-8)+ LOG [X/ (.05-X)]
8.00=7.46+LOG [X/(.05-X)]
.544=LOG[X/(.05-X]
TO GET RID OF LOG, RAISE 10^.544
3.5=X/(.05-X)
3.5(.05-X)=X
.175-3.5X=X
.175=3.5X+X
.175=X(3.5+1)
.175=4.5X
X=.0388 mol
.0388mol x (1 L/ .100 mol)=3.9 L
1000 mL x 0.05M = 50 millimols.
x mL x 0.1M = ? mmols.
-----------------
............HOCl + OH^- ==> OCl^- + H2O
initial.....50......0........0........0
add.................x................
change......-x....-x.........x........x
equil.......50-x....0.........x........x
I used 3E-8 for Ka for HOCl
pH = pKa + log(base)/(acid)
8.00 = 7.52 + log(x)/(50-x)
Solve for x = millimols OH^- added. Then mL = mmols/M. I get approximately 380 mL
I believe you made a slight error in the last calculation from mmol --> mol. The answer should be around 3.8L.
To determine the volume of 0.0100 M NaOH needed to achieve a pH of 8.00 when added to 1.00 L of 0.0500 M HOCl, we need to understand the reactions occurring and how they affect pH.
The pH scale is a measure of the concentration of hydrogen ions (H+) in a solution. A higher concentration of H+ ions results in a lower pH, indicating acidity. On the other hand, a lower concentration of H+ ions leads to a higher pH, indicating alkalinity or basicity.
In this case, we are dealing with a solution of HOCl (hypochlorous acid) and want to increase its pH from its original value by adding NaOH (sodium hydroxide). Sodium hydroxide is a strong base that reacts with the weak acid, HOCl, to form water and a salt (sodium hypochlorite).
The balanced chemical equation for this reaction is as follows:
HOCl + NaOH ⟶ NaOCl + H2O
Since the molar ratio between HOCl and NaOH is 1:1, the moles of NaOH needed to neutralize the moles of HOCl can be determined by stoichiometry.
1. Calculate the moles of HOCl in 1.00 L of 0.0500 M solution:
Moles of HOCl = concentration (M) × volume (L)
Moles of HOCl = 0.0500 M × 1.00 L
2. Determine the moles of NaOH required to react with the moles of HOCl based on the stoichiometry of the balanced equation.
3. Calculate the volume of 0.0100 M NaOH needed to obtain the desired pH of 8.00.
Volume of NaOH = moles of NaOH / concentration (M)
By following these steps, you can find the specific volume of 0.0100 M NaOH needed to achieve a pH of 8.00 when added to 1.00 L of 0.0500 M HOCl.