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A duma bulb full of air weighs 22.567 gm...

A duma bulb full of air weighs 22.567 gm at `20^@C` and 755 mm pressure. Full of vapours of a substance at `120^@C` and the same pressure. It weighs 22.8617 gm. The capacity of the bulb is 200 ml. Find out the molecular mass of the substance. [density of air `=0.00129(gm)/(ml)`]

Text Solution

Verified by Experts

`{:("volume of bulb"=200ml,,V_2=?),(T_1=(20+273)=293K,,T_2=273K),(P_1=755mm,,P_2=760mm):}}` STP conditions
so, `V_2=`volume of bulb at STP
`=(200xx755)/(293)xx(273)/(760)=185.122ml`
mass of air `=V_2xx0.00129=185.122xx0.00129`
`=0.2388gm`
mass of empty bulb `=(22.567-0.2388)`
`=22.3282gm`
mass of vapours `=(22.8617-22.3282)`
`=0.5335gm`
Let the volume of vapours at STP be V.
`V=(200xx755)/(393)xx(273)/(760)=138ml`
molecular mass of the substance
`=("mass of vapours")/("volume of vapours at STP")xx22400`
`=(0.5335)/(138)xx22400=86.69`
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