What mass of NaOH in 0.5L of water can make a pH of 13?
We know that pH + pOH = 14
If pH = 13, then pOH = 14-13 = 1
pOH is defined as pOH = -log[OH]
We need to solve for the [OH]:
1 = -log[OH]
-1 = log[OH]
10^(-1) M = [OH]
0.1 M = [OH]
Now we have the molarity of the solution. We need 0.1 M OH- in the solution.
Since NaOH is a strong base, it completely dissociates in water:
NaOH ---> Na+ + OH-. There's no equilibrium here. It's a complete dissociation. So all of the NaOH in solution is in the form of OH-.
We case use the molarity and the volume to find moles of NaOH:
0.1 mol/L NaOH * (0.5L) = 0.05 moles NaOH needed
Now, use the molecular mass of NaOH to find the number of grams you need:
0.05 moles NaOH * (40 g/mole NaOH) = 2 g of NaOH needed
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