A student collected the following data as part of the Determination of KXO_3: a.

Question

A student collected the following data as part of the Determination of KXO_3: a. Determine the pressure of oxygen alone in the cylinder. b. Determine the moles of oxygen collected. c. Determine the moles of KXO_3, at the beginning of the reaction d. Determine the identity of the halogen, X, and provide the formula for the unknown. A student collected the following data as part of the Determination of KClO_x: a. Determine the moles of O_2 collected and the moles of monoatomic oxygen, O. b. Determine the mass of O2 and of KCl at the end of the reaction. c. Determine the mole ratio of O to KCl and provide the formula for the unknown. Why is it necessary to wait for the test tube to cool before measuring the volume of oxygen collected? A student performing this experiment reads the volume of oxygen with the water level inside the graduated cylinder higher than the water level of the water bath. How does this affect her calculation of moles of O_2, and, in the second part of the experiment, her mole ratio of O to KCl?

Explanation / Answer

Q1.

a)

Pressure of Oxygen in cylinder...

Ptotal = Pgas + Pvapor

Pgas = Ptotal - Pvarpo = 751-21.068 = 729.932 torr or O2

b)

now,

PV = nRT

n = PV/(RT) = (729.932)(54*10^-3)/(62.4*(23+273))

n = 0.0021340 moles of gas, assume this is only oxygen

c)

ratio is:

KXO3 = KX + 3/2O2

then, 1 mol of KXO3 = 1.5 mol of O2

0.0021340 mol of O2 = 1/(1.5)*0.0021340 = 0.0014226 mol of KXO3

d)

Find X,

MW = mass/mol = (0.320)/0.0014226 = 224.94 g/mol

MW = K+ X+O3 = 39.9 + X + 3(16) = 224.94

x = 224.94 -3*16 - 39.9 = 137.04

best fit is iodine:

KIO3

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