Question

An ionic compound formed by a cation of radius 120pm and an anion radius 230pm will probably form a: (hint: calculate the difference in radius of cation and anion, compare to the examples in the "Course Materials")

	A.	rock salt structure
	B.	zinc-blende structure
	C.	cesium chloride structure
	D.	fluorite structure What is the rms velocity of H2O at 25oC? A. 482 m/s B. 20.3 m/s C. 643 m/s 50 ml of O2 is collected over water at 1.20 atm and 50oC.   Calculate the volume of O2(dry) at STP. A. 150 mL B. 148 mL C. 137 mL pls show solutions

Answer 1

RMS velocity of water at 25oC :   Ans = C

   T = 25oC = 25 + 273 K = 298 K

   R = universal gas constant = 8.314 J/K/mol

M = molar mass of water = 18 g/mol = 0.018 kg/mol

Hence,

RMS velocity = [3RT/M]^1/2

                    = [3x 8.314 J/K/mol x 298 K/0.018 kg/mol]^1/2

                    = 643 m/s

Therefore,

RMS velocity of water = 643 m/s

Volume of O2 (dry) at STP: Ans = C

At 50 oC , vapor pressure of water = 92 torr = 92/760 atm = 0.12 atm

Hence, pressure of O2, P = 1.2 atm - 0.12 atm = 1.08 atm

Initial:

P1 = 1.08 atm

V1 = 150 mL

T1 = 50oC = 323 K

At STP :

P2 = 1 atm

V2 = ?

T2 = 323 K

We know that

P1V1/T1= P2V2/T2

1.08 atm x 150 mL / 323 K = 1 atm x V2 / 273 K

Then,

V2 = 137 mL

Therefore,

volume of O2(dry) at STP = 137 mL