What is the pH of a solution formed by mixing 400 mL of 0.025 M HCl with 600 mL of 0.015 M NaOH?
NaOH + HCl ==> H2O + NaCl
mols HCl = M x L = ?
mols NaOH = M x L = ?
Subtract, the excess will b either acid or base. If acid, then pH = -log(HCl) = ?
If base, then pOH = -log(NaOH), then pH + pOH = pKw = 14. Solve for pH.
To determine the pH of the solution formed by mixing HCl and NaOH, we need to understand the concept of neutralization reaction.
When we mix an acid (HCl) and a base (NaOH), they react and form water (H2O) and a salt (NaCl). The reaction can be represented as:
HCl + NaOH → H2O + NaCl
In this reaction, HCl is a strong acid, while NaOH is a strong base. These strong substances fully ionize in water, which allows us to calculate the concentration of hydrogen ions (H+) and hydroxide ions (OH-) in the resulting solution, based on the stoichiometry of the reaction.
Step 1: Calculate the moles of HCl and NaOH.
Moles of HCl = Volume (in L) × Concentration (in M)
= 0.400 L × 0.025 M
= 0.010 mol
Moles of NaOH = Volume (in L) × Concentration (in M)
= 0.600 L × 0.015 M
= 0.009 mol
Step 2: Determine the limiting reactant.
To determine the limiting reactant, we compare the number of moles of each reactant. In this case, HCl and NaOH have a 1:1 stoichiometric ratio, so whichever reactant has fewer moles is the limiting reactant.
Since we have 0.010 mol of HCl and 0.009 mol of NaOH, NaOH is the limiting reactant.
Step 3: Determine the excess reactant.
The excess reactant is the one that is not fully consumed in the reaction. In this case, HCl is the excess reactant.
Step 4: Calculate the concentration of the resulting salt.
Since the reaction between HCl and NaOH produces NaCl, we need to calculate the concentration of NaCl.
The total volume of the solution is the sum of the volumes of HCl and NaOH:
Total volume = 400 mL + 600 mL = 1000 mL = 1.000 L
Moles of NaCl = Moles of limiting reactant (NaOH) = 0.009 mol
Concentration of NaCl = Moles of NaCl / Total volume
= 0.009 mol / 1.000 L
= 0.009 M
Step 5: Calculate the concentration of H+ ions.
Since HCl is a strong acid, it fully dissociates in water, releasing one H+ ion for each HCl molecule.
Concentration of H+ ions = Concentration of excess HCl = Concentration of HCl
= 0.025 M
Step 6: Calculate the concentration of OH- ions.
Since NaOH is a strong base, it fully dissociates in water, releasing one OH- ion for each NaOH molecule.
Concentration of OH- ions = Concentration of limiting reactant (NaOH)
= 0.015 M
Step 7: Calculate the pH of the solution.
pH is a measure of the concentration of H+ ions in a solution. The pH scale ranges from 0 to 14, with values below 7 being acidic, above 7 being basic, and 7 being neutral.
Since the concentration of H+ ions is known to be 0.025 M, we can calculate pH using the formula:
pH = -log[H+]
pH = -log(0.025)
≈ 1.60
Therefore, the pH of the solution formed by mixing 400 mL of 0.025 M HCl with 600 mL of 0.015 M NaOH is approximately 1.60.