Ethanol can be used in place of mercury in manometers when small pressure change

Question

Ethanol can be used in place of mercury in manometers when small pressure changes are to be measured. What is the pressure of an oxygen sample in mm of ethanol of its pressure is 58.5 mm Hg? (density of ethanol = 0.789 g/mL; density of Hg = 13.6 g.mL) A sample of methane gas, CH_4(g), occupies a volume of 60.3 L at a pressure of 469 torr and a temperature of 29.3degreeC. What would be its temperature at a pressure of 243 torr and volume of 60.3 L? A sample of oxygen gas has its absolute temperature halved while the pressure of the gas remained constant. If the initial volume is 400. mL, what is the final volume? You fill a balloon with 2.50 moles of gas at 28degreeC at a pressure of 1.20 atm. What is the volume of the balloon? When 0.72 g of a liquid is vaporized at 110degreeC and 0.967 atm, the gas occupies a volume of 0.559 L. The empirical formula of the gas is CH_2. What is the molecular formula of the gas? A mixture containing 5.38 g of CH_4(g), 1.35 g Ne(g), and 1.03 g Ar(g) is confined in a 7.00 L vessel at 25degreeC. Calculate the partial pressure of each of Neon in the mixture. Calculate the total pressure of the mixture. Partial pressure of neon Total pressure

Explanation / Answer

For your first question we can use the following expression:

P1/d1 = P2/d2
58.5/13.6 = P2/0.789
P2 = 0.789*(58.5/13.6)
P2 = 3-3938 mm ethanol

For your second question, calculate first the moles of sample, and then the temperature: PV = nRT --> n = PV/RT

n = 60.3 * (469/760) / 0.0821*(29.3+273) = 1.5

T2 = 60.3 * (243/760) / 1.5*0.0821
T2 = 156.56 K

For your third question, we know that the sample have the same pressure in both cases, while temperature is halved and volume change. We can assume that the number of moles remains the same too, so, let's write and expression for both cases of P and then solve for V2:

P1 = P2 = P; n = n; T1 = T/2; T2 = T

P1 = nRT/2*V1
P2 = nRT/V2

nRT/2V1 = nRT/V2
V2 = 2V1
V2 = 2 * 400 = 800 mL

The other three questions post them in another question thread.

Hope this helps

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