4. Calculate the density of ammonia gas, NHs, at 27 C and 635 torr mela 1.00 5.

Question

4. Calculate the density of ammonia gas, NHs, at 27 C and 635 torr mela 1.00 5. A 1.00 liter container is evacuated until the pressure is 1.00 x 10 atm at 22°C. How ma molecules of gas remain in the container? Hint: first determine the number of moles of g present! 6. A 12.5 liter scuba diving tank contains a helium-oxygen (heliox) mixture made up of 24.2 grams of He and 4.32 grams of O2 at 298 K. Calculate the mole fraction and partial pressure of each component in the mixture and the total pressure of the mixture. Express the pressures in units of atmosphere.

Explanation / Answer

4)

P= 635.0 torr

= (635.0/760) atm

= 0.8355 atm

T= 27.0 oC

= (27.0+273) K

= 300 K

Molar mass of NH3,

MM = 1*MM(N) + 3*MM(H)

= 1*14.01 + 3*1.008

= 17.034 g/mol

Lets derive the equation to be used

use:

p*V=n*R*T

p*V=(mass/molar mass)*R*T

p*molar mass=(mass/V)*R*T

p*molar mass=density*R*T

Put Values:

0.8355 atm *17.034 g/mol = density * 0.08206 atm.L/mol.K *300.0 K

density = 0.578 g/L

Answer: 0.578 g/L

5)

Given:

P = 1.0E-6 atm

V = 1.0 L

T = 22.0 oC

= (22.0+273) K

= 295 K

find number of moles using:

P * V = n*R*T

0 atm * 1 L = n * 0.08206 atm.L/mol.K * 295 K

n = 4.13*10^-8 mol

Number of molecules = number of moles * Avogadro’s number

= 4.13*10^-8 * 6.022*10^23 molecules

= 2.49*10^16 molecules

Answer: 2.49*10^16 molecules

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