.01M 100ml HCN mix with .02M 500ml NaOH find final PH of soln

To determine the final pH of a solution formed by mixing 0.01 M HCN (hydrocyanic acid) with 0.02 M NaOH (sodium hydroxide), we need to analyze the reaction that occurs between the acid and the base. This involves calculating the moles of each reactant, understanding the neutralization reaction, and then finding the resulting pH of the solution.

Step 1: Calculate Moles of HCN and NaOH

First, we need to find out how many moles of HCN and NaOH are present in their respective solutions.

• For HCN:
  • Concentration = 0.01 M
  • Volume = 100 mL = 0.1 L
  • Moles of HCN = Concentration × Volume = 0.01 mol/L × 0.1 L = 0.001 moles
• For NaOH:
  • Concentration = 0.02 M
  • Volume = 500 mL = 0.5 L
  • Moles of NaOH = Concentration × Volume = 0.02 mol/L × 0.5 L = 0.01 moles

Step 2: Determine the Reaction

HCN is a weak acid, and NaOH is a strong base. When they are mixed, they will react according to the following equation:

HCN + NaOH → NaCN + H2O

In this reaction, one mole of HCN reacts with one mole of NaOH to produce sodium cyanide (NaCN) and water. Since we have 0.001 moles of HCN and 0.01 moles of NaOH, NaOH is in excess.

Step 3: Calculate Remaining Moles After Reaction

After the reaction, we can determine the remaining moles of each substance:

• Moles of HCN remaining = 0.001 - 0.001 = 0 moles
• Moles of NaOH remaining = 0.01 - 0.001 = 0.009 moles

Step 4: Calculate the Final Volume of the Solution

The final volume of the solution after mixing is the sum of the volumes of the two solutions:

Final Volume = 100 mL + 500 mL = 600 mL = 0.6 L

Step 5: Calculate the Concentration of Remaining NaOH

Now, we need to find the concentration of the remaining NaOH in the final solution:

Concentration of NaOH = Moles of NaOH remaining / Final Volume = 0.009 moles / 0.6 L = 0.015 M

Step 6: Determine the pH of the Solution

Since NaOH is a strong base, we can calculate the pOH first and then find the pH:

pOH = -log[OH⁻] = -log[0.015] ≈ 1.83

Now, we can find the pH using the relationship between pH and pOH:

pH + pOH = 14

pH = 14 - pOH = 14 - 1.83 ≈ 12.17

Final Result

The final pH of the solution after mixing 0.01 M HCN with 0.02 M NaOH is approximately 12.17. This indicates that the solution is basic due to the excess NaOH present after the neutralization reaction.