1.

Oxygen is present in a one-litre flask at a pressure of 7.6 xx 10^(-10) mm Hg. Calculate the number of oxygen molecules in the flask at 0^(C).

Answer»

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SOLUTION :`p = 7.7 XX 10^(-10)` ATM
`= 0.01 xx 10^(-10)` atm (760 mm = 1 atm)
`T = (0+273) = 273 K`
We have,
pV = nRT
`0.01 xx 10^(-10) xx 1 = n xx 0.0821 xx 273, therefore n = (10^(-12))/(0.0821 xx 273)`
`therefore` no. of oxygen molecules = mole `xx` Av. const.
`= (10^(-12))/(0.0821 xx 273) xx 6.022 xx 10^(23)`
`= 2.68 xx 10^(10)`.


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