IGCSE Pressure Question: How many balloons can be inflated?

[UnknownGuy]

Hi, very quick question... It does like this: Helium in a cylinder (Which will be used to inflate a number of balloons) has a volume of (6*10^-3) cubic meters and a pressure of (2.75*10⁶)Pa. The pressure in each of the helium balloons is (1.1*10⁵)Pa, and the volume of each balloon (3*10^^-3) cubic meters.The temperature of helium does not change. How many balloons were inflated?

-How i solved it: Pressure * Volume = Constant so... (6.0*10^-3)*(2.75*10^6)=V₂*1.1*10^5... V₂= 0.15m³... Now what i did here was divide the total volume of helium at 1.1*10⁵ by the volume of helium in each balloon and so...0.15/3*10^-3... My answer was 50 balloons.

-Mark scheme has the following answer: (0.15-(6*10^-3))/3*10^-3... Can someone tell me where i went wrong?
Thanks in advance.

 

[gneill]

Do you expect the helium cylinder to be completely empty after all the balloons that can be inflated are inflated?

 

[UnknownGuy]

Do you expect the helium cylinder to be completely empty after all the balloons that can be inflated are inflated?

If the volume of helium in the balloon is 0.15m³ at that pressure, then why not? We use all the 0.15m³ because 0.15 is divisible by 0.030 without any remainders...

 

[gneill]

If the volume of helium in the balloon is 0.15m³ at that pressure, then why not? We use all the 0.15m³ because 0.15 is divisible by 0.030 without any remainders...

So the final pressure in the cylinder will be zero? A perfect vacuum? How does the last of the gas get moved to balloons where the pressure will be nonzero?

 

[UnknownGuy]

So the final pressure in the cylinder will be zero? A perfect vacuum? How does the last of the gas get moved to balloons where the pressure will be nonzero?

Ah, now I understand.. Thank you very much!

 

[gneill]

 

[Pegasus]

Do you expect the helium cylinder to be completely empty after all the balloons that can be inflated are inflated?

Yes just like in electricity questions we ignore resistance

 

[kuruman]

Yes just like in electricity questions we ignore resistance

Please note that this thread is more than 6 years old. Also note that in electricity questions we don't usually ignore resistance, especially when there is current flowing.

 

[haruspex]

Yes just like in electricity questions we ignore resistance

Your analogy does not work. The balloon filling problem is more akin to charging capacitors from a given capacitor.
And the correct answer to @gneill's question is no. Or were you being sarcastic?