Question

What is the ph of a 0.320 m solution of ca(no₂)₂ (ka of hno₂ is 4.5 × 10⁻⁴)?

Answer 1

To find the pH of a 0.320 M solution of Ca(NO2)2, one must calculate the Kb of NO2− from the given Ka of HNO2, then calculate the concentration of OH− to eventually determine the pH.

Step-by-step explanation:

To calculate the pH of a 0.320 M solution of Ca(NO2)2 we must first consider that calcium nitrite dissociates into Ca2+ ions and NO2− ions in solution. The NO2− ions come from nitrous acid, HNO2, which has a given Ka of 4.5 × 10∓4. Since Ca2+ is a spectator ion and does not affect pH, we focus on the NO2− ion.

The reaction of nitrite ion with water to produce nitrous acid and OH− will determine the pH:

NO2− (aq) + H2O (l) ⇌ HNO2 (aq) + OH− (aq)

To find the pH, we need to first calculate the Kb of nitrite ion from the given Ka of nitrous acid using the relation Kw = Ka × Kb. Here, Kw is the ion product constant for water at 25°C, which is 1.0 × 10−14. After finding Kb, we can then calculate the concentration of OH− ions produced and from there determine the pOH and subsequently the pH.

Answer 2

8.58

Step-by-step explanation:

-You can find this answer by first finding the Kb of the base in this situation, which will be the NO2 ion. It is important to note that while you have .32M of the salt it dissociates to form .64M of the NO2 ion. From this, you can set up your Kb equation.

-Your Kb equation is your conjugate acid concentration (HNO2) times your hydroxide concentration (OH-) divided by your final nitrite ion (NO2-) concentration.

-Based on the ICE table we can approximate these values, the hydroxide and conjugate acid concentrations will both increase by x from nothing, so the final value will be x for each of them. From this, we can tell that the final nitrite ion concentration must be the initial .64M minus this x value.

-You can then use the quadratic formula to get the final hydroxide value of 3.77122*10^-6, we can find the pOH by using the -log(x) function which gives a pOH of 5.4235.

-The pH of a solution is going to be equal to 14-pOH, or 14-5.4235 = 8.58

Have a nice day :)