1A. A child releases a balloon filled with 0.450 L of He on a day when the atmos

Question

1A. A child releases a balloon filled with 0.450 L of He on a day when the atmospheric pressure was 755 mmHg. when the balloon reaches its peak height, the air pressure is 510 mmHg. CALCULATE the new volume of the balloon. (Assume no temperature change)

1B. If no temperature of the balloon in the question above initially 26.3 Celcius, how many moles of gas are in the balloon? (Use initial values)

2A. An unknown gas occupies 125 mL at 600 mmHg and 25 Celcius. Calculate the number of moles in this sample of gas.

2B. If the gas in thiscontainer has a mass of 0.286g, what is the molar mass of the gas?

Explanation / Answer

1)

A)
Given:
Vi = 0.450 L
Pi = 755 mmHg
Pf = 510 mmHg

use:
Pi*Vi = Pf*Vf
755.0 mmHg * 0.450 L = 510.0 mmHg * Vf
Vf = 0.6662 L
Answer: 0.666 L

B)
Given:
P = 755.0 mm Hg
= (755.0/760) atm
= 0.9934 atm
V = 0.45 L
T = 26.3 oC
= (26.3+273) K
= 299.3 K

find number of moles using:
P * V = n*R*T
0.9934 atm * 0.45 L = n * 0.08206 atm.L/mol.K * 299.3 K
n = 1.82*10^-2 mol
Answer: 1.82*10^-2 mol

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