Question

Nitrate salts (NO3), when heated, can produce nitrites (NO2) plus oxygen (O2). A sample of potassium nitrate is heated, and the 02 gas produced is collected in a 700 mL flask. The pressure of the gas in the flask is 2.7 atm, and the temperature is recorded to be 329 K. The value of R= 0.0821 atm L/(mol K) How many moles of O2 gas were produced? moles After a few hours, the 700 mL flask cools to a temperature of 293K. What is the new pressure due to the O2 gas?

Answer 1

Answer: a) 0.070 moles of oxygen were produced.

b) New pressure due to the oxygen gas is 2.4 atm

Explanation:

According to ideal gas equation:

$PV=nRT$

P = pressure of gas = 2.7 atm

V = Volume of gas = 700 ml = 0.7 L

n = number of moles = ?

R = gas constant =$0.0821Latm/Kmol$

T =temperature = 329 K

$n=\frac{PV}{RT}$

$n=\frac{2.7atm\times 0.7L}{0.0821 L atm/K mol\times 329K}=0.070moles$

Thus 0.070 moles of oxygen were produced.

When the 700 mL flask cools to a temperature of 293K.

$PV=nRT$

$P=\frac{nRT}{V}$

$P=\frac{0.070\times 0.0821\times 293}{0.7}$

$P=2.4atm$

The new pressure due to the oxygen gas is 2.4 atm