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Montano1993 [528]
2 years ago
13

A 3.00 g sample of unknown hydrocarbon is prepared for combustion analysis. after the hydrocarbon undergoes complete combustion,

8.80 g of co2 and 5.40 g of h2o are produced. what is the empirical formula of the unknown?
Chemistry
1 answer:
zmey [24]2 years ago
7 0

Answer:

CH₃.

Explanation:

  • The complete combustion of hydrocarbon in an excess of oxygen produces CO₂ and H₂O according to the general reaction equation:

CₐHₓ + O₂(excess) → b CO₂ + c H₂O,

Where a is the no. of C atoms in the unknown hydrocarbon.

x is the no. of H atoms in the unknown hydrocarbon.

b is the no. of moles of CO₂ produced from the combustion of unknown hydrocarbon.

c is no. of moles of H₂O produced from the combustion of unknown hydrocarbon.

  • We can calculate b and c using the relation:

n = mass / molar mass.

  • n of CO₂ = (8.80 g) / (44.0 g/mol) = 0.2 mol.

Every molecule of CO₂ contains 1 C atom, so no. of moles of C atoms in CO₂ and thus in the original hydrocarbon is 0.2 mol.

  • n of H₂O = (5.40 g) / (18.0 g/mol) = 0.3 mol.

Every molecule of H₂O contains 2 H atoms, so no. of moles of H atoms in H₂O and thus in the original hydrocarbon is (2 x 0.3) 0.6 mol.

  • The ratio of C to H in the unknown hydrocarbon is (0.2): (2 x 0.3) = 0.2: 0.6.
  • Dividing by the lowest no. of moles (0.2) that of C.

∴ The ratio of C to H in the unknown hydrocarbon is 1: 3.

<em>So, the empirical formula of the unknown hydrocarbon is CH₃.</em>

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1.15 g of a metallic element needs 300 cm3 of oxygen for complete reaction, at 298 K and 1 atm
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X (+) + O2 (g) ---> X2O          or   


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4X(3+) + 3O2(g) ---> 2X2O3


 
In the first case, 1 mol of metal react with 1 mol of O2(g); in the second case, 2 moles of metal react with 1 mol of O2(g); in the third, 4 moles of X react with 3 moles of O2(g)



So, lets probe those 3 cases.


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That does not correspond to any of the metal with valence 1+


So, now probe the case 2.



4) Case 2:


2moles X metal / 1 mol O2(g) = x / 0.01226 mol


=> x = 2 * 0.01226 = 0.02452 mol


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That does not correspond to any metal.


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