30 grams of limestone was dissolved in hydrochloric acid, while gas was released, which was completely

| September 4, 2021 | education

30 grams of limestone was dissolved in hydrochloric acid, while gas was released, which was completely absorbed by 200 grams of 10% sodium hydroxide solution. Find the mass fraction of calcium carbonate in limestone.

Let’s write down the reaction equations:
CaCO3 + 2HCl = CaCl2 + H2O + CO2 ↑
CO2 + 2NaOH = Na2CO3 + H2O
Let’s start with the second equation:
Determine the mass of pure sodium hydroxide in solution:
m (NaOH) = w (NaOH) * m (solution) / 100% = 10 * 200/100 = 20 g.
It can be seen from the reaction equation that:
ν (NaOH) / 2 = ν (CO2)
m (NaOH) / 2 * M (NaOH) = V (CO2) / Vm (CO2)
Determine the molar mass of sodium hydroxide:
M (NaOH) = 23 + 16 + 1 = 40 g / mol
Determine the volume of carbon dioxide by expressing from the equation:
V (CO2) = m (NaOH) * Vm (CO2) / 2 * M (NaOH)
Substitute the numerical values:
V (CO2) = m (NaOH) * Vm (CO2) / 2 * M (NaOH)) = 20 * 22.4 / 2 * 40 = 5.6 liters.
Now let’s move on to the first reaction:
It can be seen from the reaction equation that:
ν (CaCO3) = ν (CO2)
m (CaCO3) * M (CaCO3) = V (CO2) / Vm (CO2)
Determine the molar mass of calcium carbonate:
M (CaCO3) = 40 + 12 + 16 * 3 = 100 g / mol
Determine the mass of calcium carbonate by expressing from the equation:
m (CaCO3) = M (CaCO3) * V (CO2) / Vm (CO2)
Substitute the numerical values:
m (CaCO3) = M (CaCO3) * V (CO2) / Vm (CO2) = 100 * 5.6 / 22.4 = 25 g.
w (CaCO3) = m (CaCO3) * 100% / m (extract) = 25 * 100% / 30 = 83.3%
Answer: the mass fraction of calcium carbonate is 83.3%.



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