The stages for preparing a pure sample of sodium nitrate are given below. 1. Titrate until the end-point is reached using dilute nitric acid. 2. Heat to evaporate water and make the solution more concentrated. 3. Wash out the conical flask. 4. Put in indicator. 5. Use a pipette to transfer a measured volume of aqueous sodium hydroxide into a conical flask. 6. Allow to cool, then filter off the crystals. 7. Carry out the procedure again with the same volumes of aqueous sodium hydroxide and dilute nitric acid, but without indicator. Which sequence of steps is correct?
- A1 → 7 → 5 → 4 → 2 → 6 → 3
- B3 → 5 → 7 → 1 → 2 → 4 → 6
- C4 → 1 → 3 → 5 → 2 → 6 → 7
- D5 → 4 → 1 → 3 → 7 → 2 → 6