In one glass - 100,0 mL 0,100M KOH solution, in other - 100,mL 0,100M HNO2 solution. What is pH of solution, which was get when both solutions were mixed up (consider that V of forthcoming solution is sum of original solutions - 200,0 ml)
The KOH and HNO2 exactly neutralize each other and the pH at the equivalence point is the pH of the hydrolyzed salt. It has a concn of 0.1M x (100 mL/200mL) = 0.05M
............NO2^- + HOH ==> HNO2 + OH^-
initial.....0.05.............0.......0
change.......-x..............x........x
equil......0.05-x............x........x
Kb for NO2^- = (Kw/Ka for HNO2) = (HNO2)(OH^-)/(NO2^-)
Substitute into the Kb expression above and solve for x = (OH^-), then convert to pH.
Why concentration of salt is 0,05?
To find the pH of the solution obtained by mixing the 0.100M KOH and 0.100M HNO2 solutions, we need to understand the chemical reaction that occurs when these two solutions are mixed.
When KOH (potassium hydroxide) and HNO2 (nitrous acid) are combined, they react to form water (H2O) and the salt potassium nitrite (KNO2). The balanced chemical equation for this reaction is:
KOH + HNO2 → KNO2 + H2O
In this reaction, the KOH acts as a base, while HNO2 acts as an acid. The resulting solution will be basic due to the presence of the remaining OH- ions from KOH.
To calculate the pH of the resulting solution, follow these steps:
Step 1: Calculate the moles of KOH and HNO2 in the original solutions.
- Moles of KOH = Molarity (0.100M) × Volume (100.0 mL) ÷ 1000 (to convert mL to L)
- Moles of HNO2 = Molarity (0.100M) × Volume (100.0 mL) ÷ 1000
Step 2: Determine the limiting reactant by comparing the moles of KOH and HNO2. The reactant with fewer moles will be the limiting reactant, and the other reactant will be in excess.
Step 3: Use the stoichiometry of the balanced equation to determine the moles of the products (KNO2 and H2O) formed. Since the reaction is 1:1, the moles of KNO2 formed will be the same as the moles of the limiting reactant.
Step 4: Calculate the new concentration of KNO2 in the mixed solution.
- Concentration of KNO2 = Moles of KNO2 ÷ Volume of the mixed solution (200.0 mL) × 1000 (to convert L to mL)
Step 5: Calculate the pOH of the solution using the concentration of OH- ions from KNO2.
- pOH = -log10[OH-]
Step 6: Calculate the pH of the solution using the relationship between pH and pOH.
- pH = 14 - pOH
By following these steps, you can determine the pH of the solution obtained by mixing the given KOH and HNO2 solutions.