The mass of a balloon is 0.02g before it is filled with air. After it is blown up with air the mass is 0.04g. Assuming oxygen makes up 21% of air, calculate the number of moles of oxygen in the balloon.

After the balloon has been blown up with air it increased its size by 0.02 g (Final mass - initial mass = mass of the air).We are told that of oxygen takes up 21% of air. Therefore, we need to work out 21% of the mass of the air in the balloon (0.02g) 0.21 x 0.02 g = 0.0042 g of oxygen in the balloonNow, we can work out how many moles are there in 0.0042 g from the mole equation Therefore,n = 0.0042 g / Mr of O2 n = 0.0042 g / 16 x 2 g per moln = 0.00013125 molesNOTE: We have to remember that oxygen in air always exists as diatomic molecule (O2) because it's more stable. Therefore, we need to multiply Mr of Oxygen by 2.

Answered by Greta S. Chemistry tutor

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