pH of:
2.50mL of 0.100M nitric acid added to 30mL of 0.200M potassium hydroxide
Please show me working out :)
To find the pH of a solution resulting from the reaction between nitric acid (HNO3) and potassium hydroxide (KOH), we need to determine the concentration of the resulting species after the reaction occurs.
Step 1: Write the balanced chemical equation for the reaction:
HNO3 + KOH → KNO3 + H2O
Step 2: Determine the limiting reactant.
Since we know the initial concentrations and volumes of both nitric acid (HNO3) and potassium hydroxide (KOH), we can determine which one will be completely consumed during the reaction.
First, calculate the number of moles for each reactant:
Number of moles of HNO3 = Molarity × Volume
= 0.100 M × 0.00250 L
= 0.000250 moles
Number of moles of KOH = Molarity × Volume
= 0.200 M × 0.0300 L
= 0.00600 moles
In this case, the number of moles of HNO3 (0.000250 moles) is smaller than the number of moles of KOH (0.00600 moles). Therefore, HNO3 is the limiting reactant, meaning it will be completely consumed, and there will be an excess amount of KOH remaining after the reaction.
Step 3: Determine the number of moles and the concentration of the excess reactant.
Since the number of moles of KOH is larger than the number of moles of HNO3 in this reaction, there will be excess KOH left over.
Excess moles of KOH = Number of moles of KOH - Number of moles of HNO3
= 0.00600 moles - 0.000250 moles
= 0.00575 moles
To calculate the concentration of the excess KOH, divide the number of moles by the final volume:
Concentration of excess KOH = Excess moles of KOH / Final volume
= 0.00575 moles / (2.50 mL + 30 mL)
= 0.168 M
Step 4: Calculate the concentration of the resulting salt, potassium nitrate (KNO3).
The balanced chemical equation shows that for every 1 mole of HNO3, 1 mole of KNO3 is produced. Since the number of moles of HNO3 is smaller (limiting reactant), the number of moles of KNO3 will be the same.
Thus, the concentration of KNO3 is also 0.000250 moles / (2.50 mL + 30 mL) = 0.00735 M.
Step 5: Calculate the concentration of H3O+, which represents the acidity of the resulting solution.
Since potassium nitrate (KNO3) is a salt, it will dissociate in water, resulting in the release of K+ ions and NO3- ions. However, the nitrate ion (NO3-) does not contribute to the acidity of the solution. Therefore, the concentration of H3O+ comes from the dissociation of water.
As we know that water dissociates to give H3O+ and OH- ions, the concentration of H3O+ is equal to the concentration of OH-, which can be calculated from the excess KOH:
Concentration of H3O+ = Concentration of OH- = 0.168 M
Step 6: Calculate the pH of the resulting solution.
The pH is calculated using the formula: pH = -log[H3O+]
pH = -log(0.168) ≈ 0.774
Therefore, the pH of the resulting solution is approximately 0.774.