A. When calcium metal reacts with water, the gas evolved will not catch fire, but the same gas evolved on Potassium metal to water catches fire. Why? b. An element forms an oxide X2O3 which is acidic in nature. Identify A as a metal or non-metal and write its molecular formula

a. Due to the evolved hydrogen from potassium to water reaction being able to reach the flash point of the reaction temperature

b. Non-metal

The molecular formula is N₂O₃

Explanation:

a. The heat of the reaction between calcium and water is given as follows

Ca + 2 H₂O → H₂ +  Ca(OH)₂    ΔH = -431.15 kJ which is exothermic, Entropy = -125.29 J/K

The heat of the reaction between potassium and water is given as follows

2 k + 2 H₂O → 2 KOH  + H₂ ΔH = -393.15 kJ Entropy = 44.91 J/K

Therefore, the reaction between potassium and water occurs more vigorously than the reaction between calcium and water such that the flash point for the released hydrogen gas is reached in the case of potassium

b. The acidic oxides are oxides of metals or non-metals that react with water to produce an acid

Given the valence of the oxide which is +3, the oxide can be aluminium, Al or nitrogen, N, however, Al₂O₃ behaves both as an acid and a base, therefore, the likely candidate is nitrogen, which shows that X is a non-metal

The molecular formula is therefore;

N₂O₃

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