Answer:
Step-by-step explanation:
The balanced chemical equation for the reaction between magnesium carbonate and hydrochloric acid is:
MgCO3 + 2HCl → MgCl2 + H2O + CO2
From the equation, we can see that 1 mole of magnesium carbonate reacts with 2 moles of hydrochloric acid to produce 1 mole of carbon dioxide. The molar mass of magnesium carbonate is 84.3 g/mol, which means that 21 g of magnesium carbonate is equal to 0.25 moles (21/84.3). Therefore, 0.25 moles of magnesium carbonate will react with 0.5 moles of hydrochloric acid to produce 0.25 moles of carbon dioxide.
The volume of carbon dioxide can be calculated using the ideal gas law, which is PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. Assuming standard temperature and pressure (STP) of 273 K and 1 atm, we can use the molar volume of a gas at STP, which is 22.4 L/mol, to calculate the volume of carbon dioxide produced.
V = n × 22.4 L/mol
V = 0.25 mol × 22.4 L/mol
V = 5.6 L
Therefore, the volume of carbon dioxide produced when 21 g of magnesium carbonate reacts completely with excess hydrochloric acid is 5.6 L. The answer is option A, 4 dm³, which is approximately equal to 5.6 L.