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#### cindy

• Guest
« on: June 03, 2004, 07:26:39 PM »
ALright, any help would be amazing   2 questions:

1.  A student reacts a sample of calcium carbide with water to produce acetylene (ethene) gas. HOw will this student need to correct his measurements when he tries to determine the number of moles of gas produced?

2. A scuba diver is swimming  30.0 m below the surface of the water. At the depth the pressure of the water is 4.0 atm and the temperature is 8.0°C. A bubble of air with a volume of 5.0 mL escapes from a divers mask. what will the volume of the gas in the bubble be after it breaks  open on the surface? The atmospheric pressure is 101.3 kPa and the temperature of the air is 24°C

Thanks so much

#### Corvettaholic

• Guest
« Reply #1 on: June 03, 2004, 07:35:03 PM »
Let me take a crack at #2, its been 5 years since I've dealt with this kind of stuff.

Lets see... pressure * volume = constant * (whatever R stands for) * temperature.

ignore the depth, I don't think it applies here, just the other numbers. Lets ignore whatever "R" is, cause I don't remember, and the other chem guys will let us know if I got it right. So 4 * 5 = c * 8. therefore the constant would be 2.5. I know its supposed to be something else, but bear with me. I'm just using plain algebra on this. So take 2.5, and plug it into the end result. (101.3kpa = 1 atm by the way, just remembered that) 1 * volume = 2.5 * 24. More algebra: volume should equal 60 ml.

Does this sound good to everyone else?

#### cindy

• Guest
« Reply #2 on: June 03, 2004, 07:47:15 PM »
OK, i THINK:

R= 0.0826

& that the temperature needs to be converted to K so T= 281 K

#### Corvettaholic

• Guest
« Reply #3 on: June 03, 2004, 07:49:09 PM »
Well just resetup the equation like I did, but make sure you multiply the right side by that value of R for both equations. You should get a different answer I think. Take my numbers for temperature, convert to kelvins, and the rest of the process is the same. Hey I learned something too

#### cindy

• Guest
« Reply #4 on: June 03, 2004, 07:53:38 PM »
Thanks!

And, do you mean both sides of the one equation or did i miss that there's actually 2 equations?

#### billnotgatez

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« Reply #5 on: June 03, 2004, 10:50:37 PM »
Hint on scuba diver
Using the ideal gas law formula
PV=nRT

Given that P1 * V1 = n1 * R * T1 is the first situation
Given that P2 * V2 = n2 * R * T2 is the second situation

We can derive P1 * V1 / T1 = n1 * R
We can derive P2 * V2 / T2 = n2 * R

Since in this situation n1 = n2
And R is the same constant for both equations

Therefore
P1 * V1 / T1 = P2 * V2 / T2

Since the unknown is V2 convert equation to

P1 * V1 * T2 /  T1 * P2 = V2