1.

3.28 g of a sample of pure copper when heated in presence of oxygen of some time forms black copper oxide (CuO) which weighs 3.92 g. What approximate percent of copper remains unoxidized?

Answer»

`4.6%`
`5.6%`
`6.6%`
`7.6%`

Solution :`{:(2Cu+O_(2)rarr,2CuO),(2xx6.5g,2(63.5+16)),("= 127 G"," = 159 g"):}`
3.92 g CuO will be obtained by oxidation of Cu
`=(127)/(159)xx3.92=3.13`
Cu LEFT unoxidized = 3.28 - 3.13 = 0.15 g
`THEREFORE %" of Cu left unoxidized"`
`=(0.15)/(3.28)xx100=4.57~=4.6`


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