A highway maintenance team compared salts used to prevent ice forming on a bridge. Each salt was spread in the same mass onto separate trays containing crus...
Question 1 Report
A highway maintenance team compared salts used to prevent ice forming on a bridge. Each salt was spread in the same mass onto separate trays containing crushed ice at -3 degrees C. The table shows results after ten minutes. The salts form ions when they dissolve in the thin layer of water on the ice.
| salt | formula | mass of ice melted / g | conductivity of a 1.0 mol dm-3 solution / S m-1 |
|---|---|---|---|
| sodium chloride | NaCl | 42 | 10.8 |
| magnesium chloride | MgCl2 | 58 | 19.6 |
| potassium chloride | KCl | 39 | 12.1 |
(a) Which salt melted the greatest mass of ice? [3]
(b) Give the formulae of the ions present in a solution of magnesium chloride. [3]
(c) State the total number of chloride ions formed when one formula unit of magnesium chloride dissolves. [3]
(d) Complete the word equation for the reaction of sodium with chlorine:
sodium + chlorine → __________ [3]
(e) Explain why solutions of all three salts conduct electricity. [4]
Answer Details
(a) Magnesium chloride melted the greatest mass of ice: 58 g, which is greater than 42 g and 39 g. [3]
(b) Magnesium chloride dissolves to give Mg2+ ions and Cl- ions. [3]
(c) One formula unit is MgCl2, so it contains 2 chloride ions. [3]
(d) sodium + chlorine → sodium chloride. [3]
(e) Each salt dissolves to form ions. Ions are charged and, in solution, are free to move. Their movement carries electrical charge, so all three solutions conduct electricity. [4]
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