Hydrochloric acid, HCl, reacts with barium hydroxide, Ba(OH)2, as shown. 2HCl(aq) + Ba(OH)2(aq) -> BaCl2(aq) + 2H2O(l) A sample of 25.0 cm³ of 0.0500 mol/dm³ Ba(OH)2 is placed in a beaker. Dilute HCl is added slowly, from a burette, to the Ba(OH)2(aq) in the beaker. A pH probe is used to measure the pH of the solution in the beaker until a total of 40.0 cm³ of dilute HCl is added. The table shows how the pH of the solution in the beaker changes. | volume of dilute HCl added/cm³ | pH of the solution in the beaker | |---|---| | 0.0 | 13.0 | | 5.0 | 12.9 | | 10.0 | 12.5 | | 15.0 | 11.6 | | 20.0 | 7.0 | | 25.0 | 3.0 | | 30.0 | 1.6 | | 35.0 | 1.1 | | 40.0 | 0.9 |

1. (a)Explain, in terms of the ions present, why the pH of the solution in the beaker changes from 13.0 to 0.9.[2]
2. (b)Use the data in the table to state the volume of dilute HCl that just neutralises all of the sample of Ba(OH)2(aq). volume of dilute HCl .............................................................. cm³[1]
3. (c)Use your answer to (b) to calculate the concentration, in mol/dm³, of the dilute HCl. concentration of dilute HCl .............................................. mol/dm³[3]

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