Question

choose which of the following are oxidation - reduction reactions. (select all that apply.)
ohcl(g) + nh₃(g) → nh₄cl(s)
o2 cucl(aq) → cucl₂(aq) + cu(s)
osicl₄(l) + 2 h₂o(l) → 4 hcl(aq) + sio₂(s)
ozn(s) + 2 hcl(aq) → zncl₂(aq) + h₂(g)
och₄(g) + 2 o₂(g) → co₂(g) + 2 h₂o(g)

Explanation:

Step1: Determine oxidation states

• For \(O_2\) in \(OCH_4(g)+2O_2(g)\to CO_2(g)+2H_2O(g)\), \(O\) in \(O_2\) has an oxidation state of \(0\), and in \(CO_2\) and \(H_2O\) it is \(- 2\). So \(O\) is reduced. \(C\) in \(CH_4\) has an oxidation state of \(-4\), and in \(CO_2\) it is \(+4\). So \(C\) is oxidized. This is a redox reaction.
• For \(Zn(s)+2HCl(aq)\to ZnCl_2(aq)+H_2(g)\), \(Zn\) has an oxidation state of \(0\) and in \(ZnCl_2\) it is \(+2\) (oxidized). \(H\) in \(HCl\) has an oxidation state of \(+1\), and in \(H_2\) it is \(0\) (reduced). This is a redox reaction.
• For \(SiCl_4(l)+2H_2O(l)\to 4HCl(aq)+SiO_2(s)\), oxidation states of \(Si = + 4\), \(Cl=-1\), \(H = + 1\), \(O=-2\) in all species. No change in oxidation states. Not a redox reaction.
• For \(O_2CuCl(aq)\to CuCl_2(aq)+Cu(s)\), \(Cu\) in \(CuCl\) has an oxidation state of \(+1\). In \(CuCl_2\) it is \(+2\) (oxidized) and in \(Cu(s)\) it is \(0\) (reduced). This is a redox reaction.
• For \(OHCl(g)+NH_3(g)\to NH_4Cl(s)\), \(Cl=-1\), \(H = + 1\), \(N=-3\) in all species. No change in oxidation states. Not a redox reaction.

Answer:

\(OCH_4(g)+2O_2(g)\to CO_2(g)+2H_2O(g)\), \(Zn(s)+2HCl(aq)\to ZnCl_2(aq)+H_2(g)\), \(O_2CuCl(aq)\to CuCl_2(aq)+Cu(s)\)