The correct option for the placement of the base in a titration involving sodium hydroxide (NaOH) and dilute hydrochloric acid (HCl) is **C. in a burette**. ### Detailed Explanation: 1. **Understanding Titration**: - Titration is a laboratory technique used to determine the concentration of a solution by reacting it with a solution of known concentration. In this case, we are titrating hydrochloric acid (HCl) with sodium hydroxide (NaOH). - The goal is to find out how much NaOH is needed to completely neutralize a given volume of HCl. 2. **Setup of the Titration**: - In a typical titration setup, you have two main components: the titrant (the solution of known concentration) and the analyte (the solution of unknown concentration). - The titrant is usually placed in a burette, which allows for precise measurement and control of the volume being added. 3. **Why Place NaOH in the Burette?**: - **Precision**: The burette is designed for accurate dispensing of liquids. It has a stopcock that allows you to control the flow of the titrant (NaOH) drop by drop, which is crucial for determining the endpoint of the titration accurately. - **Volume Measurement**: The burette is marked with measurements, allowing you to easily read how much NaOH has been dispensed. This is important for calculating the concentration of the HCl after the titration is complete. 4. **Where to Place HCl**: - The hydrochloric acid (HCl), which is the analyte, is typically placed in a conical flask. This allows for easy swirling and mixing during the titration process, ensuring that the acid and base react thoroughly. ### Why the Other Options are Incorrect: - **A. in the beaker**: - While you could technically place NaOH in a beaker, it would not allow for the precise control needed for titration. Beakers are not designed for accurate dispensing and do not have a mechanism to control the flow of liquid. - **B. in the conical flask**: - This option is incorrect because the conical flask is where the analyte (HCl) is placed, not the titrant (NaOH). The conical flask is used to mix the solutions and observe the color change at the endpoint. - **D. in the standard flask**: - A standard flask (or volumetric flask) is used for preparing standard solutions to a specific volume. It is not suitable for titration because it does not allow for the controlled dispensing of a liquid. ### Common Pitfalls: - Students often confuse the roles of the titrant and analyte. Remember, the titrant (NaOH) goes in the burette, and the analyte (HCl) goes in the conical flask. - Not using a burette can lead to inaccurate results due to the inability to measure the volume of titrant added precisely. ### Revision Summary: - In a titration, the titrant (NaOH) is placed in the burette for precise measurement. - The analyte (HCl) is placed in the conical flask for mixing and observation. - Accurate titration requires careful control of the titrant flow to determine the endpoint. - Always remember the roles of each component in the titration setup to avoid confusion.