What mass of copper is consumed in the reaction with hydrochloric acid if 10.0 g of gas is collected?

317 g

Explanation:

Cu + 2HCl --> CuCl2 +H2

1      :     2           1 : 1

1 mole of Cu  = 63.5 g

1 mole of  H2 = 2g

1 mole  Cu produces = 1 mole of H2

63.5 g of Cu produces = 2 g of H2

So

10 g of H2 will be produced from =  (63.5/2)*10 = 317 g of Copper

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