Acid-Base Equilibrium: Calculate pH, [OH-] & % Ionization 0.12M N2H4

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OH is the negative log of OH- concentration.In summary, for a 0.12 M solution of hydrazine, the hydroxide concentration is 1.26 x 10^-6 M, the pH is 8.10, and the % ionization is 0.00105%. The pOH and pKb are not the same, with pKb being the negative log of the Kb value for a base.
  • #1
Mitchtwitchita
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The base hydrazine, N2H4, has a pKb equal to 5.90. Calculate the hydroxide concentration, the pH, and the % ionization for a 0.12 M solution.

First, is pKb the same as the pOH?

If so, pOH = -log[OH-]
5.90 = -log[OH-]
log[OH-] = -5.90
=10^-5.90
[OH-]=1.26 x 10^-6

pH = 14.00 - pOH
=14.00 - 5.90
=8.10

% ionized = [OH-]/0.12 M X 100% = 0.00105% ?

Somehow I think I'm doing this problem wrong. Can anybody show me what the problem is?
 
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  • #2
Mitchtwitchita said:
The base hydrazine, N2H4, has a pKb equal to 5.90. Calculate the hydroxide concentration, the pH, and the % ionization for a 0.12 M solution.

First, is pKb the same as the pOH?

No. pKb is analagous to pKa. It is the negative log of Kb.
 
  • #3


Yes, pKb is the same as pOH. However, your calculations for [OH-] and pH are correct. The issue is with your calculation for % ionization. The correct formula for % ionization is the concentration of ionized species divided by the initial concentration of the compound, multiplied by 100%.

In this case, the compound is N2H4 and the ionized species is OH-. Therefore, the % ionization would be:

% ionization = ([OH-]/[N2H4]) x 100%
= (1.26 x 10^-6 M / 0.12 M) x 100%
= 0.00105%

So your calculations were correct, but you just need to use the correct formula for % ionization.
 

Related to Acid-Base Equilibrium: Calculate pH, [OH-] & % Ionization 0.12M N2H4

1. What is acid-base equilibrium?

Acid-base equilibrium refers to the balance between the concentration of protons (H+) and hydroxide ions (OH-) in a solution. This balance determines the pH, or level of acidity or basicity, of the solution.

2. How do I calculate pH?

The pH of a solution can be calculated using the formula pH = -log[H+], where [H+] is the concentration of protons in moles per liter. In the case of the given solution of 0.12M N2H4, the pH would be calculated as pH = -log(0.12) = 0.92.

3. How do I calculate [OH-]?

The concentration of hydroxide ions, [OH-], can be calculated using the formula [OH-] = 10^(-pH), where pH is the measured or calculated pH of the solution. In the given example, [OH-] would be calculated as [OH-] = 10^(-0.92) = 0.12M.

4. What is % ionization?

% ionization, also known as percent dissociation, is a measure of the extent to which a weak acid or base dissociates in a solution. It is calculated by dividing the concentration of dissociated ions by the initial concentration of the acid or base, and then multiplying by 100%. In the given example, the % ionization of the weak base N2H4 would be calculated as (% ionization) = ([OH-] / initial concentration) x 100% = (0.12M / 0.12M) x 100% = 100%.

5. What is the relationship between pH and % ionization?

The relationship between pH and % ionization is inverse. This means that as the pH increases, the % ionization decreases, and vice versa. This is because as the concentration of protons (H+) increases, the concentration of hydroxide ions (OH-) decreases, making it more difficult for the weak acid or base to dissociate. This relationship is important in understanding the strength of a weak acid or base in a solution.

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