Density Lab B

PolarFrost
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Re: Density Lab B

Post by PolarFrost » March 3rd, 2019, 11:44 am

You have a 1.00 M solution of sulfuric acid with a density of 1.08 g/mL. What is the molality of this solution, in
m? Use that the molecular weight of sulfuric acid is 98.09 g/mol.
It says answer is 1.02 m. How do you do this?

knightmoves
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Re: Density Lab B

Post by knightmoves » March 3rd, 2019, 12:19 pm

PolarFrost wrote:You have a 1.00 M solution of sulfuric acid with a density of 1.08 g/mL. What is the molality of this solution, in
m? Use that the molecular weight of sulfuric acid is 98.09 g/mol.
It says answer is 1.02 m. How do you do this?
This is outside this year's syllabus. But:

1.00 M = 1 mol sulfuric acid in 1 L of solution.
Density of solution = 1.08 g/ml, so mass of solution = 1.08 kg

1 mol of sulfuric acid (solute) has mass 98.09g, so mass of solvent (water) = (1.08 - 0.09809) kg = 0.982 kg

Molality = mols of solute per kg of solvent = 1/0.982 = 1.02 mol/kg (or 1.02 m if you insist ;) )

PolarFrost
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Re: Density Lab B

Post by PolarFrost » March 3rd, 2019, 12:36 pm

25. If you bring water to a boil, will it be more or less dense than if it was liquid?
I think it should be less dense because water expands from liquid to gas but the answer is more so i am confused
31. As temperature increase does the density of a liquid increase or decrease?
The answer is increase but shouldnt it be decrease because liquid is expanding.

Hartman
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Re: Density Lab B

Post by Hartman » March 9th, 2019, 1:47 pm

I think the question was asking volume, but they messed up. What test is this from?
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Kai0721
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Re: Density Lab B

Post by Kai0721 » March 13th, 2019, 8:39 am

19) Find the mass density of a sphere that has a 10 m diameter.

This question was on one of the tests in the test exchange and I have no idea how to solve it can someone explain why the answer is (4000/3)(pi) according to the key.
2018-19 Events: Amazing Mechatronic :P , Battery Buggy :D , ELG, :o Density Lab, :)

19alekb
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Re: Density Lab B

Post by 19alekb » March 16th, 2019, 11:44 am

Kai0721 wrote:19) Find the mass density of a sphere that has a 10 m diameter.

This question was on one of the tests in the test exchange and I have no idea how to solve it can someone explain why the answer is (4000/3)(pi) according to the key.
Equation for volume of a sphere: 4/3*Pi*r^3
Diameter of 10m means a radius of 5m.
5^3=125
4/3*125*Pi=volume
(500/3)*Pi=volume. <-- that's the volume
The person who wrote the test messed up writing the question and messed up getting the answer for the volume. The writer said to solve for mass density(which is just normal density), but they solved for volume. Solving for mass density without the mass is impossible. But, they also messed up solving for volume. They used 10m as the radius when it is actually the diameter for the sphere. The only thing you can solve for is the volume of the sphere which is what I listed how to do correctly above. Bad test writing.

sam13
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Re: Density Lab B

Post by sam13 » March 21st, 2019, 4:20 pm

gl10086 wrote:Are there certain tools or materials I need to know how to use for this event?
know about desity and how warm stuff is less dense and cool is more dense study that and you have 25% of the test.[/color]

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Re: Density Lab B

Post by sam13 » March 21st, 2019, 4:23 pm

Nba2302 wrote:Can any help me start up my studying(Im new)? What are some useful links? What is a very important thing in I need to know? where do i find density equations? :?:
https://owlcation.com/stem/The-Density- ... -Math-Help read/print this and put it in your binder

abhushan2004
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Re: Density Lab B

Post by abhushan2004 » April 30th, 2019, 7:30 pm

Anybody have some good tests? I'm not sure what exactly to expect for nationals(because the rules are quite simple). At both regionals and state, all we had to know was m/v and have some knowledge about the gas laws and archimedes principle.

19alekb
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Re: Density Lab B

Post by 19alekb » May 1st, 2019, 7:56 pm

We had a killer state test. Not going to go into detail because our state supervisor is the national one(I think). Anyone else have an impossibly hard state test as well?

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