Cacodyl, known for its unbearable garlicky odor and its use in producing cacodylic acid, a cotton herbicide, consists of 22.88% carbon, 5.76% hydrogen, and 71.36% arsenic by mass, with a molar mass of 209.96 g/mol. What is the molecular formula of cacodyl?

To determine the molecular formula of cacodyl, we'll first figure out its empirical formula, which gives the simplest whole-number ratio of the elements in the compound. After that, we'll use the given molar mass to find the molecular formula.

Step 1: Assume a 100 g sample of the compound, which makes it easy to convert the percentage composition to grams. So, we have: - 22.88 g of carbon - 5.76 g of hydrogen - 71.36 g of arsenic

Step 2: Convert the mass of each element to moles by dividing by their respective molar masses. - Moles of carbon: 22.88 g / 12.01 g/mol = 1.904 moles - Moles of hydrogen: 5.76 g / 1.008 g/mol = 5.714 moles - Moles of arsenic: 71.36 g / 74.92 g/mol = 0.952 moles

Step 3: Determine the simplest whole-number ratio of moles of each element by dividing each by the smallest number of moles calculated in Step 2. - Carbon: 1.904 / 0.952 = 2.00 - Hydrogen: 5.714 / 0.952 = 6.00 - Arsenic: 0.952 / 0.952 = 1.00

According to this ratio, the empirical formula appears to be C2H6As.

Step 4: Calculate the empirical formula mass by adding up the masses of C2H6As using the molar masses of each element. - C (12.01 g/mol) * 2 = 24.02 g/mol - H (1.008 g/mol) * 6 = 6.048 g/mol - As (74.92 g/mol) * 1 = 74.92 g/mol

The empirical formula mass is therefore: 24.02 g/mol + 6.048 g/mol + 74.92 g/mol = 104.988 g/mol.

Step 5: Finally, to find the molecular formula, we divide the molar mass of the compound by the empirical formula mass and round to the nearest whole number. - Molecular mass / empirical formula mass = 209.96 g/mol / 104.988 g/mol ≈ 2.00

Since the result is approximately 2, the empirical formula must be multiplied by 2 to find the molecular formula. Therefore, the molecular formula is: (C2H6As) * 2 = C4H12As2.

So, the molecular formula for cacodyl is C4H12As2.

Extra: Cacodyl is an organoarsenic compound that falls into a class of chemicals known as cacodylates. The empirical formula of a compound tells us the simplest integer ratio of atoms of each element in the compound, which does not necessarily reflect the actual numbers of atoms in the molecules but gives us a proportional idea. On the other hand, the molecular formula represents the actual number of atoms of each element in one molecule of the compound.

In the process of finding a molecular formula, first determining the empirical formula is crucial because it serves as the building block for calculating the actual molecular formula. If the ratio was not an even number, one would typically round to the nearest whole number or use a fractional multiplier to account for slight discrepancies due to rounding errors when converting masses to moles.

Molar mass, sometimes referred to as molecular weight, is the mass of one mole of a substance (in grams per mole) and is used to convert between the weight of a molecular or formula unit and the number of moles of that unit. The molar mass of each element is found on the periodic table and is used for calculations involving the conversion of grams to moles or vice versa.

Cacodylic acid, a derivative of cacodyl, is generated from cacodyl oxide and has applications in agriculture, especially as a herbicide. It's noteworthy for its use in chemistry history, having been involved in early studies of organic compounds containing metal, but due to toxicity and the unpleasant smell, it's not commonly used.