Find volume of pesticide after pressure decreases

In summary, the sprayer was used until the liquid level fell and the pressure of the air in the space above the liquid was reduced. The volume of the liquid that would still be in the tank when air pressure above the tank is 150KPa and all temperatures remain constant was calculated to be 2.7 litres.
  • #1
Richie Smash
293
15

Homework Statement


Here is a pesticide spray vessel, of total volume of 10 litres, containing 8 litres of pesticide.
Valve B is closed first,and the space above the air is filled with air at a pressure of 200KPa until the desired pressure is reached, and then valve A is then closed.

The sprayer is then used for sometime until the liquid level falls and the pressure of the air in the space above the liquid is reduced
Calculate the volume of the liquid that would still be in the tank when air pressure above the tank is 150KPa and all temperatures reamin constant.

Assume all pressure differences due to hydrostatic pressure of liquid to be negligible; i.e pressure at upper surface of liquid = pressure at bottom of the tank.

(Atmospheric pressure =100Kpa)

Homework Equations


P1V1=P2V2

The Attempt at a Solution


Hi I originally thought the solution would be to use Boyle's law, but I realized its for the volume of pesticide not the air.

And normally I would think, if the initial pressure of the air pumped was 200Kpa, would I have to add atmospheric pressure to that, but that can't be since it's in a container?
I'm very stumped as this is one of my worst areas in physics.

*high school level*
 

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  • #2
I think you are supposed to assume that those are absolute pressures.
 
  • #3
Here is my attempt, I use boyle's law to find out how much litres of air is left after the spraying is done.
250000Pa*0.002m3=150000Pa*V2

V2= 0.0027m3 =2.7 litres

Therefore that is the volume of the air after.

Since the air previously was 2 litres, and the pesticide was 8, to find out how much pesticide remains I would just do 8L-0.7L = 7.3L

SO my answer is 7.3L, I'm not sure if it is correct.
 
  • #4
Looks good.
 
  • Like
Likes Richie Smash

Related to Find volume of pesticide after pressure decreases

1. How does pressure affect the volume of pesticide?

According to Boyle's Law, the volume of a gas decreases as the pressure on it increases, and vice versa. This means that as the pressure on the pesticide decreases, its volume will increase.

2. Why is it important to calculate the volume of pesticide after pressure decreases?

Knowing the volume of pesticide after a decrease in pressure is important for accurately determining the amount of pesticide needed for a specific area. This can help prevent overuse or underuse of pesticide, which can have negative consequences for the environment and crops.

3. How can I calculate the volume of pesticide after pressure decreases?

To calculate the volume of pesticide after pressure decreases, you can use the formula V2 = V1 x P1/P2, where V2 is the new volume, V1 is the initial volume, P1 is the initial pressure, and P2 is the final pressure.

4. What units should be used for volume and pressure in the calculation?

The units used for volume and pressure can vary depending on the system of measurement being used. However, it is important to ensure that both volume and pressure are using the same units in order to get an accurate result. Common units for volume include liters, gallons, and cubic meters, while common units for pressure include atmospheres, pascals, and pounds per square inch.

5. Can this calculation be used for any type of pesticide?

Yes, the calculation for finding the volume of pesticide after pressure decreases can be used for any type of pesticide. However, it is important to note that the initial volume and pressure may vary depending on the specific pesticide being used and the conditions it is stored in.

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