1. A sample of Br2(g) takes 18.0 min to effuse through a membrane. How long woul

Question

1. A sample of Br2(g) takes 18.0 min to effuse through a membrane. How long would it take the same number of moles of Ar(g) to effuse through the same membrane? Answer: _____ min

2. Ne(g) effuses at a rate that is ______ times that of Br2(g) under the same conditions. Answer: Rate(Ne) / Rate Br2 = ________

3. If He(g) has an average kinetic energy of 6350 J/mol under certain conditions, what is the root mean square speed of N2(g) molecules under the same conditions? Answer: ________m/s

4. A gas mixture is made by combining 7.2 g each of Ar, Ne, and an unknown diatomic gas. At STP, the mixture occupies a volume of 17.07 L. What is the molar mass of the unknown gas? Answer: ______ g/mol Identify the unknown gas: ________________.

5. Use the van der Waals equation of state to calculate the pressure of 2.30 mol of H2O at 485 K in a 5.10-L vessel.  Answers:  P=______atm.  Now use the ideal gas equation to calculate the pressure under the same conditions.  P= _______atm.

Explanation / Answer

a. 9min

b.Graham's Law

r1 / r2 = ?(MM2 / MM1)

We will set the rate of Br2 to be 1 and assign it to r2. That will put it in the denominator and make r1 be how many times faster the Cl2 effuses.

x / 1 = ?(159.808 / 70.906)

x = 1.50

c.

Ek(He) = 6350 = 1,5RT
T = 432,2 K

Vrms (Cl2) = sqrt((3R*432,2)/71*10^-3) m/s = 390 m/s

d.

Moles of Ne =7.2 /20 0.305
Moles of Ar=7.2/40 0.1525

Volume of Ne =22.4 x 0.305 6.832
Volume of Ar =22.4 x 0.1525 3.416L

Volume of unknown gas =17.7-10.248 =6.822

Moles of unkown gas =6.822/22.4 0=.304mol

Molecular mass M of unknown gas=
7.2/0.304=23.68

Diatomic gas having a close mass for above value is Oxygen.So gas is Oxygen

e.

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