Density Lab B

[azboy1910]

Let's get this marathon started!

1. A floating object displaces 40 g of liquid when placed in a tub full of it. What is its weight, in N?
2. What is the force required to hold a floating ball with a diameter of 5 mm and a mass of 25 g underwater (freshwater)?
3. 50 mL of water is poured into a cup. A person drinks 35 mL of it, and then places an object with a mass of 2 g in it. The object is completely submerged, and the water level has risen to 16.5 mL. What is the object's density in g/cc?

[YellowMamba]

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 1. Less than 392.4 N. 3. Assuming cc is cubic centimeters (correct me if I am wrong), 1.333 g/cc

On 2 are you holding the ball in the air?

[azboy1910]

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 1. Less than 392.4 N. 3. Assuming cc is cubic centimeters (correct me if I am wrong), 1.333 g/cc

On 2 are you holding the ball in the air?

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1. The correct answer is 0.392 N, and when rounded to significant figures is 0.4 N. 

40 g / 1000 = .04 kg

.04 kg x 9.81 m/s^2 = 0.392 N

2. Since the ball already has a density greater than freshwater, there is no force required to hold the ball underwater. Hence, the answer here is 0 N.

3. Correct. If this was rounded to significant figures, the answer would be 1 g/cc.

Your turn!

[YellowMamba]

A container of gas has a volume of 8 liters at one atmosphere of pressure and 40˚ Celsius. The temperature is then lowered to -40 Celsius, and the container is compacted to 4.2 liters. What is the final pressure in kPa? (6 sig figs)

[azboy1910]

Since no one has answered yet,

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Answer: 143.965 kPa

Where 1 atm = 101.325 kPa, 40 degrees C = 313.15 K , and -40 degrees C = 233.15 K.

[YellowMamba]

Correct! Your turn.

[azboy1910]

1. If the radius of x atom is 70.0 pm, what is the total volume of of these atoms in ?
2. Calculate the ppb of a 10.0% salt by mass saltwater soultion.
3. The temperature of a gas is at 40 K at the moment and currently has a volume of 13.3 L. The temperature of the gas is increased by the same temperature of the boiling point of water. Calculate the new volume of the gas in .

[YellowMamba]

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1. Assuming the atom is a perfect sphere: 0.0010262536 m3 5.0286426e^-24
2. 100,000,000 ppb
3. 46550 cm3

[azboy1910]

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1. Assuming the atom is a perfect sphere: 0.0010262536 m3
2. 100,000,000 ppb
3. 46550 cm3

So here's what I got, please feel free to tell me if you disagree:

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[YellowMamba]

Here’s my work for 1 and 3. Correct me if I am wrong:

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1: 
70 picometers = 7e^-11
Volume of a sphere = 4/3(pi)(r
4/3(pi)(3.43e^-31) = approximately 1.436755e^30
That is the volume of one atom.
1.436755e^-30(3.50)(10^6) = 5.0286426e^-24
I recalculated and got 5.0286426e^-24. I guess I forgot to cube the radius length.

3:
40K and 13.3L to 140K and xL
By Charles’s Law I got (13.3)(140) = 40x
Solve for x:
1862 = 40x
46.55 = x
This is how many liters.
To convert to cm3
1L = 1000mL = 1000cm3
So I got 46550 cubic cm.