A student investigates the reaction between aqueous sodium carbonate and two different solutions of dilute hydrochloric acid, labelled $$\(\mathbf{A}\)$$ and $$\(\mathbf{B}\)$$. The student does three experiments. Experiment 1 - Rinse a burette with distilled water and then with dilute hydrochloric acid $$\(\mathbf{A}\)$$. - Rinse a conical flask with distilled water. - Fill the burette with dilute hydrochloric acid A. Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. - Record the initial burette reading. - Use a measuring cylinder to pour $$\(25 \mathrm{~cm}^{3}\)$$ of aqueous sodium carbonate into the conical flask. - Add five drops of methyl orange indicator to the conical flask. - Stand the conical flask on a white tile. - Slowly add dilute hydrochloric acid $$\(\mathbf{A}\)$$ from the burette to the conical flask, while swirling the flask, until the solution becomes orange. - Record the final burette reading. Experiment 2 - Refill the burette with dilute hydrochloric acid A. Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. - Record the initial burette reading. - Empty the conical flask and rinse it with distilled water. - Use the measuring cylinder to pour $$\(25 \mathrm{~cm}^{3}\)$$ of aqueous sodium carbonate into the conical flask. - Add five drops of thymolphthalein indicator to the conical flask. - Stand the conical flask on a white tile. - Slowly add dilute hydrochloric acid $$\(\mathbf{A}\)$$ from the burette to the conical flask, while swirling the flask, until the solution becomes colourless. - Record the final burette reading. Experiment 3 - Repeat Experiment 1, using dilute hydrochloric acid B instead of dilute hydrochloric acid $$\(\mathbf{A}\)$$. Explain why a white tile is used during the titration. ................................................................................................................................................ . ..........................................................................................................................................

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