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A student set-up the apparatus below in order to determine the percentage by volume of oxygen in air.
a) Why did water rise when the reaction had stopped?
b) The student wrote the expression for the percentage by volume of oxygen in air as
#(y-x)/x times 100%#
Why the volume of oxygen was calculated using the above expression incorrect?
c) What should have been done after the reaction had stopped

Answer Text:
a).To occupy space previously occupied by oxygen that was used by smoldering Phosphorous.
b).Because oxides of phosphorous formed still occupy space enviously occupied by oxygen.
#(P_2O_5, P_2O_3)#
c).Let all the fumes dissolve in water before final reading is taken.