A research group tested a lithium-containing powder for use in a lightweight oxygen sensor. The powder was made by heating lithium metal in a controlled sup...
Question 1 Report
A research group tested a lithium-containing powder for use in a lightweight oxygen sensor. The powder was made by heating lithium metal in a controlled supply of oxygen gas. Fig. 1 shows the outer-shell electron arrangement before ionic bonding. The product was stored in a sealed tube because it reacts with water to form an alkaline solution.
(a) State the number of electrons in the outer shell of a lithium atom. [3]
(b) Complete the formula of lithium oxide, using the ion charges Li+ and O2-. [4]
(c) Give the name of the force holding lithium ions and oxide ions together. [3]
(d) When lithium oxide is added to water, state the pH range expected for the solution. [3]
(e) Write a balanced chemical equation, including state symbols, for the reaction of lithium with oxygen to make solid lithium oxide. [4]
Answer Details
(a) A lithium atom has 1 electron in its outer shell. [3]
(b) Two Li+ ions are needed to balance one O2- ion, so lithium oxide is Li2O. [4]
(c) The ions are held together by electrostatic attraction: attraction between oppositely charged lithium and oxide ions. [3]
(d) Lithium oxide reacts with water to make an alkaline solution, so its pH is greater than 7, for example in the range pH 10 to 14. [3]
(e) Balance lithium atoms and oxygen atoms, including states:
\[4\mathrm{Li(s)} + \mathrm{O_2(g)} \rightarrow 2\mathrm{Li_2O(s)}\]
There are four Li atoms and two O atoms on each side. [4]
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