Question

The decomposition of H2CO3(aq) gives off CO2(g) and also produces H2O(l). In a particular experiment at 30.0ºC, 184.3 mL of gas product at 1.078 atm were collected over water. What mass in mg of H2CO3 reacted? Enter your answer to 2 decimal places

Answer 1

Pressure (P) = 1.078 atm

Temperature (T) = 30 ^oC = (273 + 30) = 303 K

Gas constant (R) = 0.082 atm L/mol

For 1 mole CO₂

PV = RT

V = (0.082 x 303)/1.078

   = 23.048 L

   = 23048 mL

Volume of 1 mol CO₂ at 30.0ºC and 1.078 atm = 23048 mL

From the above equation it is clear that 1 mole H₂CO₃ on decomposition gives 1 mol CO₂.

Molar mass of H₂CO₃ = 2 x 1 + 1 x 12 + 3 x 16 = 2 + 12 + 48 = 62 g/mol

23048 mL CO₂ is going to be produced when 62 g H₂CO₃ reacted

184.3 mL CO₂ is going to be produced when (62 g x 184.3 mL)/23048 mL H₂CO₃ reacted

                                                                      = 0.49577 g H₂CO₃ reacted

                                                                      = 495.77 mg H₂CO₃ reacted   ( As 1 g = 1000 mg)

Therefore the mass of H₂CO₃ reacted = 495.77 mg