A student collects oxygen gas produced by the thermal decomposition of potassium…
CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
A student collects oxygen gas produced by the thermal decomposition of potassium chlorate in an inverted graduated cylinder filled with water. The water bath and gas sample reach thermal equilibrium at 22∘C. Immediately after collection, the water levels inside and outside the cylinder are equal, and the barometric pressure in the laboratory is 751mmHg. The vapor pressure of water at 22∘C is 19.8mmHg.
(a) Identify the two gaseous components present in the collection cylinder at the moment the measurement is taken.
(b) Using kinetic–molecular reasoning, explain why the measured pressure inside the cylinder must be corrected before the amount of oxygen can be calculated.
(c) If the student ignored the need for any pressure correction, would the calculated number of moles of oxygen be too large, too small, or correct? Justify your choice qualitatively.