Question

A.What concentration of potassium hydroxide is needed to give an aqueous solution with a pOH of 3.720?
Molarity of potassium hydroxide =

B.What concentration of sodium hydroxide is needed to give an aqueous solution with a pH of 9.210?

Molarity of sodium hydroxide =

Answer 1

A.What concentration of potassium hydroxide is needed to give an aqueous solution with a pOH of 3.720?
Molarity of potassium hydroxide = 1.91*10^-4 M

Solution :-

Given data

pOH= 3.720

formula to calculate the pOH is as follows

pOH = -log[OH-]

rearranging this formula we get

[OH-] = antilog[- pOH]

Lets put the value of the pOH in the formula and calculate the [OH-]

[OH-] =antilog [-3.72]

[OH-] = 1.91*10^-4 M

Mole ratio of the OH- to KOH is 1 :1

Therefore the concentration of the KOH needed = 1.91*10^-4 M

B.What concentration of sodium hydroxide is needed to give an aqueous solution with a pH of 9.210?

Molarity of sodium hydroxide =

Solution :-

Given data

pH= 9.210

[NaOH] = ?

Lets convert the given pH to pOH

pH+ pOH = 14

pOH = 14 – pH

pOH = 14 – 9.210

pOH = 4.79

now lets calculate the concentration of the [OH-] using the pOH

Formula to calculate the pOH is as follows

pOH = -log[OH-]

Rearranging this formula we get

[OH-] = antilog[- pOH]

Let’s put the value of the pOH in the formula and calculate the [OH-]

[OH-] =antilog [-4.79]

[OH-] = 1.62*10^-5 M

Mole ratio of the OH- to NaOH is 1 :1

Therefore the concentration of the NaOH needed = 1.62*10^-5 M