Question

Which of the following statements is(are) true? Correct the false statements.

a. When a base is dissolved in water, the lowest possible pH of the solution is 7.0.

b. When an acid is dissolved in water, the lowest possible pH is 0.

c. A strong acid solution will have a lower pH than a weak acid solution.

d. A 0.0010-M Ba(OH)₂ solution has a pOH that is twice the pOH value of a 0.0010-M KOH solution

Short answer

1. When base is dissolved in water the minimum pH is 7.1.
2. When acid is dissolved in water the lowest pH is 0.
3. Strong acid have pH lower than weak acid, so this is correct.
4. The [OH^-] concentration of 0.0010 M Ba(OH)₂ is twice than 0.0010 M KOH not the pH.

Step-by-step solution

Lowest Possible Value when Base is Dissolved in Water

When base is dissolved in water the minimum pH is 7.1 because 7 pH suggest the neutral solution not a basic solution. Thus, given statement is incorrect.

Lowest Possible Value when Acid is Dissolved in Water

For an acid the pH varies from 0 to 7, hence lowest value when acid is dissolved in water is 0 and maximum is 6.99. Thus, given statement is correct.

Strong Acid and Weak Acid 

If we [H⁺] value is known pH can be calculated as

${\text{pH=-log[H}}^{\text{+}}\text{]}$

So, the higher the value of[H⁺] ions lower will be the pH. As, Strong acid dissociates more as compared to weak acid so it has more [H⁺] ions as compared to weak.

Thus, strong acid has lower pH than a weak acid. Thus, this statement is correct.

pOH of Two Different Bases

Ba(OH)₂ dissociates as :

${\text{Ba(OH)}}_{\text{2}}\to {\text{Ba}}^{\text{2+}}{\text{+2OH}}^{\text{-}}$

1 mole of Ba(OH)₂ gives 2 moles of OH^-, So, 0.0010 M Ba(OH)₂ will give 0.002 moles of OH^-,

${\text{pOH=-log[OH}}^{-}\text{]=-log\hspace{0.17em}0.002=2.7}$

KOH dissociates as:

$\text{KOH}\to {\text{K}}^{\text{+}}{\text{+OH}}^{\text{-}}$

From the equation we can say that, 0.0010 M KOH will give 0.001 moles of OH^-,

${\text{pOH=-log[OH}}^{-}\text{]=-log\hspace{0.17em}0.001=3}$

So we can say that [OH^-] concentration of 0.0010 M Ba(OH)₂ is twice than 0.0010 M KOH not the pH.