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). 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 of the titrant being added to the analyte. 3. **Placement of Solutions**: - **Burette**: The sodium hydroxide (the base) should be placed in the burette. This is because the burette allows for accurate dispensing of the NaOH solution drop by drop, which is essential for determining the endpoint of the titration accurately. - **Conical Flask**: The dilute hydrochloric acid (the acid) is placed in the conical flask. This is where the reaction occurs, and the acid is the solution whose concentration we are trying to determine. - **Beaker**: A beaker is generally used to hold excess solutions or to prepare solutions, but it is not suitable for titration because it does not allow for precise measurement of the volume being added. - **Standard Flask**: A standard flask (or volumetric flask) is used for preparing standard solutions and is not used in titration setups. 4. **Why the Other Options are Incorrect**: - **A. in the beaker**: This option is incorrect because a beaker does not provide the precision needed for titration. You cannot control the flow of the solution accurately from a beaker. - **B. in the conical flask**: This option is incorrect because the conical flask is where the acid (HCl) is placed, not the base (NaOH). The conical flask is used to contain the solution being analyzed. - **D. in the standard flask**: This option is incorrect because a standard flask is not used in titration. It is designed for preparing solutions to a specific volume, not for dispensing them during a titration. ### Example Calculation: If you were to perform a titration, you might start with a known volume of HCl in the conical flask (e.g., 25.0 mL of 0.1 M HCl) and then slowly add NaOH from the burette until the endpoint is reached (indicated by a color change if an indicator is used). The volume of NaOH used can then be used to calculate the concentration of HCl using the formula: \[ C_1V_1 = C_2V_2 \] Where: - \(C_1\) = concentration of HCl - \(V_1\) = volume of HCl - \(C_2\) = concentration of NaOH - \(V_2\) = volume of NaOH used ### Common Pitfalls: - Not using a burette for the titrant can lead to inaccurate results due to the inability to control the volume added. - Forgetting to add an indicator can make it difficult to determine the endpoint of the titration. - Misreading the burette can lead to errors in calculating the concentration of the unknown solution. ### Revision Summary: - In titration, the base (NaOH) is placed in the burette for precise measurement. - The acid (HCl) is placed in the conical flask where the reaction occurs. - Beakers and standard flasks are not suitable for titration setups. - Accurate titration requires careful control of the volume of titrant added to reach the endpoint.