WAEC Chemistry 2012 Paper

Concept:Balancing a chemical equation requires equal numbers of each type of atom on both sides.Explanation:Given equation: $x\mathrm{CH_3OH} + y\mathrm{O_2} \rightarrow 2\mathrm{CO_2} + z\mathrm{H_2O}$Balance carbon atoms: Left has $x$ C, right has $2$ C.So, $x = 2$.Updated equation: $2\mathrm{CH_3OH} + y\mathrm{O_2} \rightarrow 2\mathrm{CO_2} + z\mathrm{H_2O}$Balance hydrogen atoms: Left has $2 \times 4 = 8$ H, right has $2z$ H.So, $2z = 8$, giving $z = 4$.Balance oxygen atoms: Left has $2 + 2y$ O; right has $4 + 4 = 8$ O.Therefore, $2 + 2y = 8$, which gives $y = 3$.Thus, $x = 2$, $y = 3$, and $z = 4$.Answer:$x, y, z$ respectively are $2, 3, 4$ (Option A).