1) A combustion device was used to determine the empirical formula of a compound

Question

1) A combustion device was used to determine the empirical formula of a compound containing only carbon, hydrogen, and oxygen. A 0.6349g of sample of the unknown produced 1.603g of CO_2 and 0.2810 g of H_2_O. Determine the empirical formula of the compound?

2) A plant makes liquid CO_2 by treating dolomitric limestone with commercial sulfuric acid. The dolomite analysis 68.0 % CaCO_3 , 30.0% MgCO, and 2,0% SiO_2; the acid is 94% H_2_SO_4 and 6% H_2_O. Calculate (a) pounds.of CO_2_ produced per ton of dolomite treated (b) pounds of acid used per ton of dolomite treated.

Explanation / Answer

1.

moles CO2 = 1.603/ 44.009 g/mol=0.03642
mass C = 0.03642 x 12.011 =0.4375 g
moles H = 2 x 0.2810 / 18.02 g/mol=0.03119
mass H = 0.03119 x 1.008 =0.03144
mass O = 0.6349 - ( 0.03144 + 0.4375)=0.166 g
moles O= 0.166 / 15.999 g/mol=0.01037

C = 0.03642/ 0.01037 =3.5
H = 0.03119/ 0.01037=3
0.01037/0.01037 = 1

to get whole numbers multiply by 2
C7H6O2 is the empirical formula

2.Look at the balanced equation for the reaction between sulfuric acid and the two carbonates of interest:

MgCO3 + H2SO4 --> MgSO4 + H2O + CO2

CaCO3 + H2SO4 --> CaSO4 + H2O + CO2

In both cases, one mole of sulfuric acid is required for each mole of carbon that is consumed. From part (i) you know that 10.358 kmol of carbon are present in each ton of dolomite, which tells you how many kilomoles of H2SO4 you need, so solve for kilograms of H2SO4 and then pounds:

10.358 kmol C x (1 kmol H2SO4 / 1 kmol C) = 10.358 kmol H2SO4

10.358 kmol H2SO4 x (98.08 kg H2SO4 / 1 kmol H2SO4) = 1015.9 kg H2SO4

1015.9 kg H2SO4 x (2.20462 lb / 1 kg) = 2239.6 lb H2SO4

Now that's how much PURE H2SO4 you'd need; as you said, the solution isn't 100% H2SO4, so we need to account for that. The percentage by weight of a solution is given by:

%w/w = (weight of solute / weight of solution) x 100

Plugging in what we know:

94% = (2239.6 lb H2SO4 / weight of solution) x 100

0.94 = 2239.6 lb H2SO4 / weight of solution

weight of solution = 2239.6 lb / 0.94 = 2382.6 lb of sulfuric acid solution.

If you wish to round the answer to two sig.figs, write it as 2.4x10^3 lb.

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