A dolomite sample weighing 10.4 g was placed in a vessel with 200 ml of 20% sulfuric acid (density 1.14 g / ml).

A dolomite sample weighing 10.4 g was placed in a vessel with 200 ml of 20% sulfuric acid (density 1.14 g / ml). Was released 4.48 liters of gas. Calculate the mass fraction of CaMg (CO3) 2 in the sample.

CaMg (CO3) 2 + 2H2SO4 = CaSO4 + MgSO4 + 2CO2 + 2H2O
m = 20.4 g
n (H2SO4) = (200 x 0.2 x 1.14) / 98 = 0.465 mol – in excess
n (CO2) = 4.48 / 22.4 = 0.2 mol
⇒ n (CaMg (CO3) 2) = 0.2 / 2 = 0.1 mol
m (CaMg (CO3) 2) = 0.1 x (24 + 40 + 2×60) = 18.4 g
ω (CaMg (CO3) 2) = 18.4 / 20.4 x 100% = 90%
Answer: the mass fraction of salt in the sample is 90%.

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