what is the pH of a solution that is 0.10 M KNO2 and 0.15 M HNO2
0.12
not even close.
Use pH = pKa + log [(base)/(acid)]
To find the pH of a solution that contains both KNO2 and HNO2, we need to consider the acid-base properties of these substances.
1. Identify the acid and base in the solution:
- HNO2 can act as both an acid and a base. In this case, we will consider it as a weak acid.
- KNO2 dissociates in water to produce NO2- ions, which can act as a weak base.
2. Write the dissociation equations:
- HNO2 (aq) ⇌ H+ (aq) + NO2- (aq)
- KNO2 (aq) ⇌ K+ (aq) + NO2- (aq)
3. Set up an ICE table for the dissociation of HNO2:
- Initial: 0.15 M HNO2, 0 M H+, 0 M NO2-
- Change: -x M HNO2, +x M H+, +x M NO2-
- Equilibrium: (0.15 - x) M HNO2, x M H+, x M NO2-
4. Write the equilibrium expression for the dissociation of HNO2:
- Ka = [H+][NO2-] / [HNO2]
5. Use the Ka expression and the equilibrium concentrations to calculate x:
- Ka = (x)(x) / (0.15 - x)
6. Since x is small compared to 0.15, we can simplify the expression:
- Ka = x^2 / 0.15
7. Use the given Ka value for HNO2 (Ka = 4.5 x 10^-4) to solve for x:
- 4.5 x 10^-4 = x^2 / 0.15
8. Solve for x:
- x^2 = (4.5 x 10^-4)(0.15)
- x = √(6.75 x 10^-5)
- x ≈ 0.0082
9. Calculate the pH using the concentration of H+ ions:
- pH = -log[H+]
- pH = -log(0.0082)
- pH ≈ 2.08
Therefore, the pH of the solution containing 0.10 M KNO2 and 0.15 M HNO2 is approximately 2.08.
To determine the pH of a solution, we need to know the acidity or basicity of the solute. In this case, we have a mixture of an ionic compound and a weak acid. The first step is to examine whether the solute species can contribute to the acidity of the solution.
KNO2 is an ionic compound consisting of a potassium cation (K+) and a nitrite anion (NO2-). Since nitrite is the conjugate base of a weak acid (HNO2), it can potentially affect the solution's pH.
HNO2 is a weak acid that can donate a proton (H+) because it only partially dissociates in water. Its conjugate base, NO2-, is the nitrite anion mentioned earlier.
To find the pH of the solution, we need to consider the acidity contribution of both KNO2 and HNO2. First, we evaluate the impact of KNO2 on the pH.
Since KNO2 completely dissociates into its constituent ions (K+ and NO2-) in water, the concentration of NO2- equals the concentration of KNO2 (0.10 M). However, because NO2- is a weak base, it can interact with water, resulting in the formation of hydroxide ions (OH-).
NO2- + H2O ⇌ HNO2 + OH-
This reaction introduces OH- ions into the solution, increasing the pH (making it more basic). Since we are looking for the pH, which measures acidity, we need to account for this increase.
Next, we examine the contribution of HNO2 to the pH. As a weak acid, HNO2 partially dissociates in water, forming H+ and NO2- ions. The concentration of HNO2 is given as 0.15 M, indicating the concentration of H+ ions.
HNO2 ⇌ H+ + NO2-
The dissociation of HNO2 generates H+ ions, which lower the pH of the solution (making it more acidic).
Taking both the HNO2 and KNO2 contributions into account, we can find the overall effect on the pH by calculating the net acidity change. We compare the contributions of the acidic HNO2 and the basic NO2- to determine the net pH.
If the concentration of H+ (0.15 M) due to the dissociation of HNO2 is greater than the concentration of OH- (formed by the interaction of NO2- with water, which equals 0.10 M), the solution will be acidic.
On the other hand, if the concentration of OH- is higher than the concentration of H+, the solution will be basic.
Therefore, to determine the pH, we need to calculate the concentrations of both H+ and OH- and compare them.