Answer:
a. The pH of a sample of lemon juice with [H⁺] = 3.8*10⁻⁴ M is 3.4, indicating acidity.
b. The pH of a commonly available window-cleaning solution with [OH⁻] = 1.9*10⁻⁶ M is 8.28, indicating basicity.
c. The [H⁺] is 1.74*10⁻⁴ M.
d. The [OH⁻] is 1.51*10⁻⁵ M.
Explanation:
pH is a measure of acidity or alkalinity that indicates the amount of hydrogen [H⁺] or hydronium [H₃O⁺] ions present in a solution or substance. Mathematically the pH is the negative logarithm of the molar concentration of the hydrogen or proton ions (H⁺) or hydronium ions (H₃O⁺):
pH= -log₁₀ [H⁺]= -log₁₀ [H₃O⁺] or pH= -log [H⁺]= -log [H₃O⁺]
The pH scale ranges from 0 to 14. Values less than 7 indicate the acidity range and those greater than 7 indicate alkalinity or basicity. Value 7 is considered neutral.
Case a
You know [H⁺]= 3.8*10⁻⁴ M. Then:
pH= -log (3.8*10⁻⁴)
pH=3.42
The pH of a sample of lemon juice with [H⁺] = 3.8*10⁻⁴ M is 3.4, indicating acidity.
Case b
Like pH, pOH (or OH potential) is a measure of the basicity or alkalinity of a solution.
The pOH indicates the concentration of hydroxyl ions [OH-] present in a solution:
pOH= -log₁₀ [OH⁻]= -log [OH⁻]
The pOH is related to the pH by the formula:
pH + pOH= 14
In this case you know [OH⁻]=1.9*10⁻⁶ M. Then:
pOH= -log(1.9*10⁻⁶)= 5.72
So pH + 5.72= 14
pH= 14 - 5.72
pH= 8.28
The pH of a commonly available window-cleaning solution with [OH⁻] = 1.9*10⁻⁶ M is 8.28, indicating basicity.
Case c
You know pH=3.76. Then:
3.76= -log [H⁺]
-3.76= log [H⁺]
[H⁺]=[tex]10^{-3.76}[/tex]
[H⁺]= 1.74*10⁻⁴ M
The [H⁺] is 1.74*10⁻⁴ M.
Case d
You know that pH + pOH=14 and pH is 9.18. Then
9.18 + pOH=14
pOH=14 - 9.18
pOH= 4.82
You know pOH= - log [OH⁻]. Then:
4.82= -log [OH⁻]
-4.82= log [OH⁻]
[OH⁻]=[tex]10^{-4.82}[/tex]
[OH⁻]= 1.51*10⁻⁵ M
The [OH⁻] is 1.51*10⁻⁵ M.
