Calculate (a) the moles and (b) the mass of magnesium carbonate at the start if 0.2 moles of sulfuric acid is added to the magnesium carbonate and the excess sulfuric acid made up to a 250 cm3 solution. 25 cm3 of this solution required 0.03 moles of sodium hydroxide for neutralisation.
MgCO3 + H2SO4 �¨ MgSO4 + H2O + CO2 H2SO4 + 2
NaOH �¨ NaCl + H2O
The question is wrong by the way, the product of H2SO4 reacting with 2 NaOH should be Na2SO4 + 2 H2O
the actual mass (g) = Number of moles x Molar mass,
or m = n x M
Number of moles of solute = Concentration (mol. L) x Volume of solution (liters) -1
or n = C x V
To calculate the moles and mass of magnesium carbonate, we need to use the balanced equation and the information provided.
The balanced equation for the reaction between magnesium carbonate (MgCO3) and sulfuric acid (H2SO4) is:
MgCO3 + H2SO4 → MgSO4 + H2O + CO2
From the equation, we can see that 1 mole of magnesium carbonate reacts with 1 mole of sulfuric acid.
(a) Calculating the moles of magnesium carbonate:
Since 0.2 moles of sulfuric acid is added, we can infer that the moles of magnesium carbonate needed to react with it will also be 0.2 moles. This is based on the stoichiometry of the balanced equation, where the mole ratio of sulfuric acid to magnesium carbonate is 1:1.
So, the moles of magnesium carbonate at the start are 0.2 moles.
(b) Calculating the mass of magnesium carbonate:
To calculate the mass, we need to know the molar mass of magnesium carbonate (MgCO3), which can be obtained from the periodic table.
The molar mass of Mg = 24.31 g/mol
The molar mass of C = 12.01 g/mol
The molar mass of O = 16.00 g/mol
To determine the molar mass of MgCO3, we add up the molar masses of the individual elements:
Molar mass of MgCO3 = (24.31 g/mol + 12.01 g/mol + (16.00 g/mol * 3)) = 84.31 g/mol
Now, we can calculate the mass of magnesium carbonate:
Mass = Moles × Molar mass
Mass = 0.2 moles × 84.31 g/mol
Therefore, the mass of magnesium carbonate at the start is 16.86 grams.
Note: Be sure to double-check the units to ensure they are consistent (e.g., convert cm3 to grams if necessary) in your specific calculations.