This reaction is used in a school demonstration of sodium metal. A very small piece of sodium is placed on water in a trough. It moves across the water, pro...
Question 1 Report
This reaction is used in a school demonstration of sodium metal. A very small piece of sodium is placed on water in a trough. It moves across the water, producing hydrogen gas and sodium hydroxide solution. Fig. 1 shows a model for sodium before it reacts. The outer electron from each sodium atom has become part of a shared group of electrons. A student uses the model to compare sodium with magnesium, which has two outer electrons per atom.
(a) Complete the word equation for the reaction.
sodium + water → sodium hydroxide + __________ [1]
(b) Give the charge on each sodium ion in Fig. 1. [1]
(c) Explain how sodium atoms form the ions and electrons shown in Fig. 1. [3]
(d) Which metal, sodium or magnesium, is expected to have stronger metallic bonding? Give a reason. [2]
(e) State two safety precautions the student should take in this reaction. [3]
Answer Details
(a) The missing product is hydrogen. [1] Sodium reacts with water to make sodium hydroxide and hydrogen gas.
(b) Each sodium ion has charge 1+. [1]
(c) Each sodium atom loses one outer electron [1]. Loss of this electron produces a Na+ ion [1], and the lost electrons become delocalised, able to move through the metal lattice. [1]
(d) Magnesium has stronger metallic bonding. [1] Each magnesium atom supplies two delocalised electrons, giving stronger electrostatic attraction between its positive ions and the electron sea than in sodium. [1]
(e) Any three suitable precautions gain the marks: use a very small piece of sodium [1], wear eye protection [1], and handle sodium with tongs/forceps [1]. Other acceptable precautions include standing behind a safety screen or well back, and storing sodium under oil before use. Sodium reacts vigorously with water and produces flammable hydrogen.
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