The allium family of vegetables, which include onion, leek, garlic and chives contain sulfur containing compounds. These chemicals are responsible for the vegetables' characteristic odour and properties. One such compound is allylmercaptan.
10.0 g of an onion extract was dissolved in water and an oxidising agent added, which converted all the sulfur in the allylmercaptan into sulfate ions.
Following this, an excess of barium nitrate was added which resulted in a precipitation of barium sulfate with no remaining sulfate ions If the mass of the precipitate obtained was 0.2336 g, what is the percent by mass of allylmercaptan in the onion extract, assuming that all of the sulfur present came from allylmercaptan ?
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To find the percent by mass of allylmercaptan in the onion extract, we need to calculate the mass of allylmercaptan and then divide it by the mass of the onion extract.
First, we need to determine the number of moles of barium sulfate precipitated by using the mass of the precipitate obtained.
The molar mass of barium sulfate (BaSO4) is:
Ba = 137.33 g/mol
S = 32.06 g/mol
O = 16.00 g/mol (four oxygen atoms)
So, the molar mass of BaSO4 is:
137.33 g/mol + 32.06 g/mol + (16.00 g/mol × 4) = 233.39 g/mol
Now, we can calculate the number of moles of barium sulfate (BaSO4):
Moles of BaSO4 = mass of precipitate / molar mass of BaSO4
Moles of BaSO4 = 0.2336 g / 233.39 g/mol
Next, we need to determine the number of moles of sulfate ions (SO4^2-) present in the onion extract because the sulfate ions come from allylmercaptan.
Since the barium nitrate was added in excess, we can assume that all the sulfate ions reacted with barium to form barium sulfate. This means the moles of barium sulfate formed are equal to the moles of sulfate ions initially present in the onion extract.
Now, we can calculate the number of moles of sulfate ions:
Moles of sulfate ions = Moles of BaSO4
Finally, we can determine the moles of allylmercaptan using the molar ratio between allylmercaptan and sulfate ions. From the chemical formula of allylmercaptan, we can see that it contains one sulfur atom per molecule.
Moles of allylmercaptan = Moles of sulfate ions
Now we can calculate the mass of allylmercaptan using the moles of allylmercaptan and the molar mass of allylmercaptan.
Mass of allylmercaptan = Moles of allylmercaptan × molar mass of allylmercaptan
Now that we have the mass of allylmercaptan, we can calculate the percent by mass of allylmercaptan in the onion extract.
Percent by mass of allylmercaptan = (Mass of allylmercaptan / Mass of onion extract) × 100
To obtain the solution, we need the molar mass of allylmercaptan. Thus, we need to refer to reliable sources for the accurate molar mass of allylmercaptan.