Density Lab B

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Fallsbury
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Re: Density Lab B

Post by Fallsbury » March 3rd, 2020, 5:20 pm

A liter of liquid nitrogen weights 807 grams and nitrogen has a molecular weight of 28 amu. If the gas is heated to 293 kelvin, what will the final volume be in liters? Assume that pressure remains at 1 atm throughout the process.

Also, can someone tell me how to hide stuff? Thx
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azboy1910
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Re: Density Lab B

Post by azboy1910 » March 4th, 2020, 1:07 pm

- Moles = 807 grams / 28 amu = 28.82 moles

Plug it in the equation:

- PV = nRT --> (1 atm)(V) = (28.82 moles)(0.0821)(293 K)
- V = 693 L (three siginificant figures)
*In order to hide text, you need to highlight your text by clicking and dragging your cursor over it. Then you need to click "answer" at the top of the screen (where bold, italize, etc. is). The reason for this is if you do this with the "hide" function, it won't work (at least for me).

Here's an example:

abcdefg (without answer fuction)

abcdefg (with answer function)
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2019 Events: Circuit Lab, Crime Busters, Density Lab
2020 Events: Circuit Lab, Codebusters (Trial), Crime Busters, Density Lab

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Re: Density Lab B

Post by Fallsbury » March 4th, 2020, 2:19 pm

Thats correct! Thanks for telling me about the hide function. If the test asked for sig figs, you would use
1 sig fig
and the correct answer would then be
700 liters
Your turn!
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azboy1910
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Re: Density Lab B

Post by azboy1910 » March 4th, 2020, 3:35 pm

Ok,

Fill in the blanks:
1) One hydrogen molecule contains _________________________ atoms.

2) At a constant temperature, pressure and volume are ______________ proportional.

3) The gas law related to #2 is called _______________________.

4) Charles' Law relates _______________ and _______________.

5) The formula for linear density is ______________________.

Complete the problems below:
1) A gas occupies a volume of 1.7 L at 1.22 atm. What is the final pressure of the gas if it expands to 2.4 L?

2) A block has a side length of 9.0 m and weighs 8000 N. A student estimates that the density of the block is 1500 kg/m^3. What is the student's percent of error?

3) A balloon has a volume of 0.30 m^3. If helium is pumped into the balloon at a rate of 0.10 m^3/s for 15 seconds, then what is the force required to lift the balloon? What is the total mass that can be lifted by the balloon?

- Density of Helium = 0.1786 g/L
- Density of Air = 1.225 kg/m^3

4) A person jumps into a pool that is filled with water all the way. After he jumps into the pool, he is completely under the water. the volume of the water displaced will be equivalent to ________________________.
a) the volume of the person
b) the volume of the person
c) 1/2 the volume of the person
d) double the volume of the person

5) A ball has a diameter of 25.0 m and weighs 800.0 kg. If it is completely submerged in a pool of mercury (13.56 g/cm^3) and attached to the bottom of the pool by a string, then what is the tension force in the string?
Jay M. Robinson Junior Varsity 2019-2020
2019 Events: Circuit Lab, Crime Busters, Density Lab
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Re: Density Lab B

Post by Garvogragus » March 7th, 2020, 3:04 pm

For Density Lab, the questions seem to consider STP to be 1atm and 273.15K. I read that STP was changed to 10^5 Pa (1 Bar). For regionals/states/nationals, should students use the new STP or the previous one. Furthermore, one mole of a gas at STP should be 22.71L with the new STP not 22.4L. Please help me clarify this for regionals.

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Re: Density Lab B

Post by azboy1910 » March 7th, 2020, 4:51 pm

For STP, I use 1 atm and 273 K, but if they tell you to use 100,000 Pa instead, you definitely should. As for molar volume at STP, I would recommend sticking to 22.4 L as this has also worked for me.
Jay M. Robinson Junior Varsity 2019-2020
2019 Events: Circuit Lab, Crime Busters, Density Lab
2020 Events: Circuit Lab, Codebusters (Trial), Crime Busters, Density Lab

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Re: Density Lab B

Post by knightmoves » March 7th, 2020, 9:21 pm

Garvogragus wrote:
March 7th, 2020, 3:04 pm
For Density Lab, the questions seem to consider STP to be 1atm and 273.15K. I read that STP was changed to 10^5 Pa (1 Bar). For regionals/states/nationals, should students use the new STP or the previous one. Furthermore, one mole of a gas at STP should be 22.71L with the new STP not 22.4L. Please help me clarify this for regionals.
You are correct that, per IUPAC, 1 bar / 22.71L has been correct since 1982. You are also correct that many people continue to use the old definition.

My advice is to use 1 bar / 22.71L, and to write something like IUPAC redefined STP in 1982 in brackets; a decent ES will always mark that correct. Unless using 22.4L gives you a round number (eg. a question producing 33.6L of gas).

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