50 cm3 of sulphur (IV) oxide were produced at s.t.p. when some quantity of powder sulphur were burnt in excess oxygen. (a) Write the equation for the reaction (b) Calculate the volume of oxygen used up during the reaction (c) Which of the gas laws is applicable? State the law.

 50 cm3 of sulphur (IV) oxide were produced at s.t.p. when some quantity of powder sulphur were burnt in excess oxygen. (a) Write the equation for the reaction (b) Calculate the volume of oxygen used up during the reaction (c) Which of the gas laws is applicable? State the law.

Solution:

(a) Equation for the reaction

      S(g)  +  O2(g) --> SO2 

(b) From the equation at s.t.p. all gases occupy 22.4 dm3 which equals 22400 cm3

So at s.t.p. 22400cm3 of SO2 required 22400 cm3 of O2.

Hence 1cm3 of SO2 will require 1cm3 of O2.

:. 50cm3 of SO2 will use 50cm3 of O2.

Or better still solve it this way

S(g)  +  O2(g) --> SO2

               v?               v

              ---               ---

              mv@stp      mv@stp

Substitute the values and cross multiply

               v                50cm3

              ---               ---

            22400cm3    22400cm3

v*22400cm3=22400cm3*50cm3

v= 22400cm3*50cm3

     ---------------------

       22400cm3

:. v=50cm3

NOTE: v represent volume, while mv represent molar volume

(c) Avogadro's law is applicable and it states that at the same temperature and pressure equal volume of gases contain the same number of molecules.

QUESTION SOURCE: WAEC 1988 QUESTION 4(a)(b)(c)