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Question:

The decomposition of a certain mass of CaCO3 gave 11.2 dm3 of CO2 gas at S.T.P. The mass of KOH required to completely neutralise the gas is:

20 g

56 g

28 g

42 g

Solution:

Weight of 11.2 dm3 of CO2 gas at STP = 44/2 = 22 g
KOH + CO2 → KHCO3
56 g 44 g
KOH required for complete neutralisation of 22g CO2 = 56/44 × 22 = 28g.