Question

Section 11 (48pts total/&pts per question) partial credit given for work shown, AND work is required for credit, even if correct answer is given. You are required to show the appropriate chemical equations for all problems involving reactions. 2.1. An instrument, maintained at 120 °C, has two separate flasks that contain different gases. If the flasks are opened so that the gases are able to mix, what is the molar mass of the final gas mixture? Flask Gas Pressure Volume (atm) (Liters) Fluorine 3.00 2.250 Chlorine 5.75 Inst 1 4.50 Answer: 2.2. What mass of potassium chlorate must be decomposed to produce 250 ml of oxygen gas collected over water at 35°C and an atmospheric pressure of 0.950 atm? (The other reaction product is solid potassium chloride.)

Answer 1

2.1) The moles of the gases present are calculated:

n F2 = P * V / R * T = 3 atm * 2.25 L / 0.082 * (120 + 273) K = 0.20 mol

n Cl2 = 5.75 * 4.5 / 0.082 * (120 + 273) = 0.80 mol

The average molar mass of the final gas is calculated:

MM ave = Xi * MMi = (0.2 * 38) + (0.8 * 71) = 64.4 g / mol

2.2) The reaction that occurs is:

2 KClO3 = 2 KCl + 3 O2

It is necessary that the vapor pressure of the water at that temperature is 0.06 atm

The moles of O2 are calculated:

n O2 = (0.95 - 0.06) * 0.25 / 0.082 * (35 + 273) = 0.0088 mol

The mass of KClO3 is calculated:

m KClO3 = 0.0088 mol O2 * (2 mol KClO3 / 3 mol O2) * (122.55 g KClO3 / 1 mol) 0.719 g

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