Question

9 mark for review
which of the following is the balanced net - ionic equation for the reaction between li(s) and water?
a ( 2 mathrm{li}(s)+2 mathrm{h}^{+}(a q)+2 mathrm{oh}^{-}(a q)
ightarrow 2 mathrm{li}^{+}(a q)+2 mathrm{oh}^{-}(a q)+mathrm{h}_{2}(g) )
b ( 2 mathrm{li}(s)+2 mathrm{h}_{2} mathrm{o}(l)
ightarrow 2 mathrm{li}^{+}(a q)+2 mathrm{oh}^{-}(a q)+mathrm{h}_{2}(g) )
c ( 2 mathrm{li}(s)+2 mathrm{h}_{2} mathrm{o}(l)
ightarrow 2 mathrm{lioh}(s)+mathrm{h}_{2}(g) )
d ( 2 mathrm{li}(s)+2 mathrm{h}_{2} mathrm{o}(l)
ightarrow 2 mathrm{lih}(s)+mathrm{h}_{2}(g) )

Explanation:

• First, let's recall the reaction of alkali metals with water. Lithium (\(Li\)) reacts with water (\(H_2O\)) to form lithium hydroxide (\(LiOH\)) and hydrogen gas (\(H_2\)).
• For option A: In water, \(H^+\) and \(OH^-\) do not exist in the form shown in this equation. Water is a weak electrolyte and should be written as \(H_2O\) in the net - ionic equation for this reaction.
• For option B: This is the correct net - ionic equation. Lithium metal (\(Li(s)\)) reacts with water (\(H_2O(l)\)). The balanced equation considering the charge and mass balance: \(2Li(s)+2H_2O(l)\to2Li^{+}(aq) + 2OH^{-}(aq)+H_2(g)\). The lithium atoms are balanced (2 on each side), hydrogen atoms: \(2\times2 = 4\) on the left (from \(2H_2O\)) and \(2 + 2=4\) on the right (\(2\) from \(2OH^-\) and \(2\) from \(H_2\)), and oxygen atoms (2 on each side).
• For option C: \(LiOH(s)\) is incorrect. In aqueous solution, \(LiOH\) dissociates into \(Li^{+}(aq)\) and \(OH^{-}(aq)\) as it is a strong base (alkali metal hydroxide) and soluble in water.
• For option D: \(LiH(s)\) is not the product of the reaction between \(Li\) and \(H_2O\). The reaction of \(Li\) with \(H_2O\) is a redox reaction where \(Li\) is oxidized (\(Li\to Li^{+}+e^{-}\)) and \(H\) in \(H_2O\) is reduced (\(2H_2O + 2e^{-}\to H_2+2OH^{-}\)).

Answer:

B. \(2Li(s)+2H_2O(l)\to2Li^{+}(aq)+2OH^{-}(aq)+H_2(g)\)