If 10.0 mL of 0.250 mol/L NaOH(aq) is added to 30.0 mL of 0.17 mol/L HOCN(aq), what is the pH of the resulting solution?
NaOH + HOCN ==> NaOCN + HOH
mols NaOH to begin = M x L = 0.250 x 0.010 = ??
mols HOCN to begin = M x L = 0.17 x 0.030 = ??
There is more HOCN than NaOH. The difference in mols is how much HOCN is left unreacted. The NaOCN formed is the amount of the lesser chemical (in this case NaOH). So you have a buffer formed consisting of a weak acid (HOCN) and its salt (NaOCN).
Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]
Post your work if you get stuck.
To find the pH of the resulting solution after the reaction between 10.0 mL of 0.250 mol/L NaOH(aq) and 30.0 mL of 0.17 mol/L HOCN(aq), follow these steps:
Step 1: Write the balanced chemical equation for the reaction between NaOH and HOCN.
NaOH(aq) + HOCN(aq) -> NaOCN(aq) + H2O(l)
Step 2: Determine the moles of NaOH and HOCN used in the reaction.
Moles of NaOH = volume (L) x concentration (mol/L)
= 0.010 L x 0.250 mol/L
= 0.0025 mol
Moles of HOCN = volume (L) x concentration (mol/L)
= 0.030 L x 0.170 mol/L
= 0.0051 mol
Step 3: Determine the limiting reagent.
The limiting reagent is the one that is completely consumed in the reaction. To find the limiting reagent, compare the moles of each compound. In this case, NaOH is the limiting reagent because it has fewer moles than HOCN.
Step 4: Use the balanced chemical equation to determine the moles of NaOCN formed.
From the balanced equation, 1 mole of NaOH reacts to form 1 mole of NaOCN.
Moles of NaOCN formed = moles of NaOH used
= 0.0025 mol
Step 5: Calculate the concentration of NaOCN.
Volume of solution = volume of NaOH + volume of HOCN
= 0.010 L + 0.030 L
= 0.040 L
Concentration of NaOCN = moles / volume (L)
= 0.0025 mol / 0.040 L
= 0.0625 mol/L
Step 6: Calculate the pOH of the resulting solution.
pOH = -log[OH-]
pOH = -log[0.0625]
pOH = 1.20
Step 7: Calculate the pH of the resulting solution.
pH + pOH = 14 (at 25 degrees Celsius)
pH + 1.20 = 14
pH = 12.80
Therefore, the pH of the resulting solution is 12.80.
To determine the pH of the resulting solution, we need to calculate the moles of HOCN and NaOH present and then determine the concentrations of each species. Finally, we can use the Henderson-Hasselbalch equation to find the pH.
Step 1: Calculate the moles of HOCN and NaOH
Moles of HOCN = volume (L) × concentration (mol/L)
Moles of HOCN = 0.030 L × 0.17 mol/L = 0.0051 mol
Moles of NaOH = volume (L) × concentration (mol/L)
Moles of NaOH = 0.010 L × 0.250 mol/L = 0.0025 mol
Step 2: Determine the concentrations of HOCN and NaOH in the resulting solution
The total volume of the resulting solution will be the sum of the initial volumes of HOCN and NaOH solutions.
Total volume = 0.030 L + 0.010 L = 0.040 L
Concentration of HOCN in the resulting solution = moles of HOCN / total volume
Concentration of HOCN = 0.0051 mol / 0.040 L = 0.1275 mol/L
Concentration of NaOH in the resulting solution = moles of NaOH / total volume
Concentration of NaOH = 0.0025 mol / 0.040 L = 0.0625 mol/L
Step 3: Use the Henderson-Hasselbalch equation to calculate the pH
Henderson-Hasselbalch equation: pH = pKa + log ([A-] / [HA])
The pKa of HOCN is needed to calculate the pH. Assuming the pKa value of HOCN is not provided, we cannot calculate the pH without this information.
Please provide the pKa value for HOCN so that I can help you calculate the pH of the resulting solution.