Q. Crude calcium carbide is made in an electric furnace by the following reaction:-

`CaO + 3C -> CaC_2 + CO`

The product contains 85% of `CaC_2 ` and 15% of unreacted `CaO.`

How much `CaO` is to be added to the furnace charge for each 1000 kg of `CaC_2`(pure) produced?

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`CaO+3C rarr CaC_2+CO`

The product contains 85% of `CaC_2` and `15%` of unreacted CaO.

This means if we take 100g of furnace charged `CaC_2` it will only contain 85g of pure `CaC_2` .

If we get 1000kg of pure `CaC_2` that accounts for 85% of the total weight of the final mixture.

Weight of final mixture `= 100/85xx1000 = 1176.47kg`

Amount of unreacted CaO `= 1176.47-1000 = 176.47kg`

`CaO+3C rarr CaC_2+CO`

Molar mass in g/(mol)

`CaO = 56`

`CaC_2 = 64`

Molar ratio

`CaO:CaC_2 = 1:1`

Amount of `CaC_2 ` produced `= (1000xx1000)/64 = 15625mol`

Amount of `CaO` needed for reaction `= 15625mol`

Mass of `CaO` need to produce `CaC_2 = 15625xx56 = 875kg`

For 100% efficient reaction we need 875kg of CaO. But here we have 176.47kg of untreated CaO.

**So amount of CaO need is 875+176.47 = 1051.47kg.**

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