A 4.28 gram sample of a gas occupies 800 mL at STP. What is its molecular weight

Question

A 4.28 gram sample of a gas occupies 800 mL at STP. What is its molecular weight? a. 60.0 g/mol b. 153.0 g/mol c. 76.5 g/mol d. 120.0 g/mol e. 140.0 g/mol A sample of hydrogen collected by displacement of water occupied 30.0 mL at 24.0 degree C on a day when the barometric pressure was 736 torr. What volume would the hydrogen occupy if it were dry and at STP? The vapor pressure of water at 24.0 degree C is 22.4 torr. a. 32.4 mL b. 21.6 mL c. 36.8 mL d. 25.9 mL e. 27.6 mL At a given temperature and pressure, the velocity of an He molecule would be _____ times the velocity of a CH_4 molecule. a. one b. two c. three d. four e. five What is the molecular weight of a (hypothetical) gas that diffuses 1.414 times faster than nitrogen, N_2? a. 14.0 g/mol b. 4.85 g/mol c. 23.5 g/mol d. 32.6 g/mol e. 46.6 g/mol Direct vaporization of a solid by heating without passing through the liquid state is: a. distillation b. evaporation c. sublimation d. impossible A gas at high pressures or low temperatures is no longer a(n): a. non-ideal gas b. supercritical fluid c. ideal gas d. standard vapor A measure of the inward attraction among liquid particles that must be overcome to expand the surface is the: a. viscosity b. surface tension c. resistance d. hydrogenbond _____ states that "A system at equilibrium responds in such a way as to undo any applied stress." a. Graham's Law b. lessthanorequalto Chatlier's Principle c. Avogadro's Law d. Dalton's Law

Explanation / Answer

7)

at STP,

P = 1 atm

T = 273 K

V = 800 mL = 0.800 L

lets find the number of mol,

use:

P*V = n*R*T

1 atm * 0.800 L = n*0.0821 atm.L/mol.K * 273 K

n = 0.0357 mol

now use:

n = mass / MM

0.0357 = 4.28/MM

MM = 120.0 g/mol

Answer: d

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