Final answer:
To determine the volume of the unknown solution of HCl used in a titration with NaOH, the concentration of HCl is calculated using the volume and molarity of NaOH that reached the endpoint, then applying the stoichiometry of the balanced chemical reaction.
Step-by-step explanation:
The volume of the unknown solution used to titrate a 25.00 ml sample of HCl is dependent on the titration process. To find the concentration of the hydrochloric acid solution, a calculation involving the volume and concentration of the sodium hydroxide solution used is necessary. For instance, if the end point of the titration occurred after adding 31.416 mL of a 0.1234 M NaOH solution, the number of moles of NaOH would equal the number of moles of HCl that was in the original solution. Thus, the concentration of HCl would be calculated by dividing the number of moles of HCl by the volume of the unknown solution (200.0 mL) in liters.
Specifically, to find the concentration of HCl:
- Calculate the moles of NaOH used: Moles NaOH = 31.416 mL * 0.1234 M = 0.003876 mol (since 1 L = 1000 mL, the volume in liters is 0.031416 L).
- Use the stoichiometry of the reaction (HCl + NaOH → NaCl + H2O), which is 1:1, to find the moles of HCl that reacted: Moles HCl = Moles NaOH = 0.003876 mol.
- Divide the moles of HCl by the volume of the HCl solution in liters to find the concentration: Concentration HCl = 0.003876 mol / 0.200 L = 0.01938 M.