Question

The density of air at STP is 1.285 g/L. Which of the following cannot be used to fill a balloon that will float in air at STP?

Answer 1

NO can't  be used to fill a balloon

Further explanation

Conditions at T 0 ° C and P 1 atm are stated by STP (Standard Temperature and Pressure). At STP, Vm is 22.4 liters/mol.

Answer options that need to be added :

a. Ne

b. NO

c. NH₃

d. CH₄

e. HF

will float in air ⇒ element or compound to fill the balloon, its density must be less than < 1.285 g/L

We can use the ideal gas formula ta find density :

$\tt \rho=\dfrac{P.MW}{RT}$

Because at STP, then the constant value is

$\tt \rho=\dfrac{1~atm\times MW}{0.08205\times 273.15~K}\\\\\rho=0.0446\times MW$

So that the density is determined from the MW(molecular weight) of each element or compound

• a. Ne

Ar = 20.1797 g/mol

$\tt \rho=0.0446\times 20.1797=0.9~g/L$

• b. NO

MW=30.006 g/mol

$\tt \rho=0.0446\times 30.006=\boxed{\bold{1.338~g/L}}$

• c. NH₃

MW=17.0306 g/mol

$\tt \rho=0.0446\times 17.0306=0.760~g/L$

• d. CH₄

MW=16.04 g/mol

$\tt \rho=0.0446\times 16.04=0.715~g/L$

• e. HF

MW=20.01 g/mol

$\tt \rho=0.0446\times 20.01=0.892~g/L$