Period 3 elements react with chlorine gas, Cl₂(g), to form chlorides. (a) The table shows the differences in observations which occur when two Period 3 chlorides are added to water. Period 3 chloride | observations when added to water | pH of solution formed with water ---|---|--- NaCl | White solid disappears. Colourless solution made. | 7 SiCl₄ | Pale yellow solution forms. Bubbles form and the test-tube feels hot. White precipitate forms. | 1-2

1. (a)(i)Write an equation for the reaction occurring when SiCl₄ is added to cold water. Include state symbols.[1]
2. (a)(ii)Name the type of reaction occurring when SiCl₄ is added to water. Ignore the exothermic/endothermic nature of the reaction.[1]
3. (a)(iii)Explain, in terms of bonding, why NaCl and SiCl₄ behave differently when added to water.[2]
4. (a)(iv)Explain, in terms of electronegativity, why the bonding in NaCl is different from the bonding in SiCl₄.[3]
5. (b)Cl₂(g) dissolves in cold water and reacts with it. Cl₂ + H₂O → HCl + HClO
6. (b)(i)Identify the oxidation number of chlorine in each of the chlorine-containing species in this reaction. chlorine-containing species | Cl₂ | HCl | HClO ---|---|---|--- oxidation number of chlorine | | |[2]
7. (b)(ii)Name the type of reaction occurring.[1]
8. (b)(iii)Explain why chlorine is used in the purification of water.[1]
9. (c)A mixture of HCl and HClO is added to cold dilute NaOH. One of the products behaves as a bleach. Suggest the equation for the reaction occurring.[2]

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