which compound contains about 27% carbon by mass?
carbon dioxide, CO2
formaldehyde, CH2O
methane, CH4
ethanol, C2H6O
Answers
There are three main types of chemical formulas:empirical, molecular and structural. Empirical formulas show the simplest whole-number ratio of atoms in a compound, molecular formulas show the number of each type of atom in a molecule,and structural formulas show how the atoms in amolecule are bonded to each other
Explanation:
The formulas we have calculated in the preceding section express the simplest atomic ratio between the elements in the compound. Such formulas are called empirical formulas. An empirical formula does not necessarily represent the actual numbers of atoms present in a molecule of a compound; it represents only the ratio between those numbers. The actual numbers of atoms of each element that occur in the smallest freely existing unit or molecule of the compound is expressed by the molecular formula of the compound. The molecular formula of a compound may be the empirical formula, or it may be a multiple of the empirical formula. For example, the molecular formula of butene, C4H8, shows that each freely existing molecule of butene contains four atoms of carbon and eight atoms of hydrogen. Its empirical formula is CH2. One molecule of ethylene (molecular formula C2H4) contains two atoms of carbon and four atoms of hydrogen. Its empirical formula is CH2. Both have the same empirical formula, yet they are different compounds with different molecular formulas. Butene is C4H8, or four times the empirical formula; ethylene is C2H4, or twice the empirical formula.
Table 6.7 shows three groups of compounds. Within each group, the compounds have the same empirical formula and percent composition but different molecular formulas. That they are different compounds is shown by their different boiling points.
TABLE 6.7 Compounds with the same empirical formula but different molecular formulas
Empirical formula Compound Molecular
formula Boiling
point, °C
CH (92.2% C; 7.8% H) acetylene C2H2 -84
benzene C6H6 80
CH2 (85.6% C; 14.4% H) ethylene C2H4 -103
butene C4H8 -6.3
cyclohexane C6H12 80.7
CH2O (40.0% C; 6.7% H;
53.3% O) formaldehyde CH2O -21
acetic acid C2H4O 117
glyceraldehyde C3H6O3 140