Considering the definition of STP conditions, 3.35 moles of helium are contained within the balloon.
The STP conditions refer to the standard temperature and pressure. Pressure values at 1 atmosphere and temperature at 0 ° C are used and are reference values for gases. And in these conditions 1 mole of any gas occupies an approximate volume of 22.4 liters.
In this case, you know that scientist fills a large, tightly sealed balloon with 75,000 mL of helium at STP.
So, you can apply the following rule of three: if by definition of STP conditions 22.4 liters are occupied by 1 mole of helium, 75 L (75 L= 75000 mL, being 1 L= 1000 L) are occupied by how many moles of helium?
[tex]amount of moles of helium=\frac{75 Lx1 mole}{22.4 L}[/tex]
amount of moles of helium= 3.35 moles
Finally, 3.35 moles of helium are contained within the balloon.
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