Question

A liquid compound X of molecular mass 18 u can be obtained from a number of natural sources. All the animals and plants need liquid X for their survival. When an electric current is passed through 200 grams of pure liquid X under suitable conditions, then 178 grams of gas Y and 22 grams of gas Z are produced. Gas Y is produced at the positive electrode whereas gas Z is obtained at the negative electrode. Moreover, gas Y supports combustion whereas gas Z burns itself causing explosions.
(a) Name (i) liquid X (ii) gas Y, and (iii) gas Z.
(b) What is the ratio of the mass of element Z to the mass of element Y in the liquid X?
(c) Which law of chemical combination is illustrated by this example?
(d) Name two sources of liquid X.
​(e) State an important use of Y in our life.

Answer 1

Liquid compound X will be water(H₂O).
When electrolysis of water is done it splits into hydrogen ion and oxygen ion. The ratio of hydrogen and oxygen is 2:1.

$$\begin{gathered} \mathrm{At}\mathrm{cathode}:2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2 \\ \mathrm{At}\mathrm{anode}:2{\mathrm{OH}}^{-}\to {\mathrm{H}}_2\mathrm{O}+\frac{1}{2}{\mathrm{O}}_2+2{\mathrm{e}}^{-} \end{gathered}$$

(a) Liquid X is Water.
Liquid Y is oxygen.
Liquid Z is hydrogen.

(b) Electrolysis of 1 mole of water produces 2 moles of hydrogen gas and 1 mole of the oxygen gas. Hence, the Ratio of mass of gases, Z and Y is 4:32 or 1:8.

(c) Law of constant proportions is illustrated by the given example.

(d) Liquid X(water) can be found in Ponds and wells.

(e) Y(Oxygen) is required for breathing.