Sulfamethoxazole has the molecular formula C10H11N3O3S.

10.0 g of tablets containing sulfamethoxazole and trimethoprim were crushed and dissolved in water. A strong oxidising agent was added, which converted all the sulfur in the sulfamethoxazole into sulfate ions.

Following this, an excess of barium nitrate was added which resulted in precipitation of barium sulfate with no remaining sulfate ions in solution.

If the mass of the precipitate obtained was 2.2758 g, what is the percent by mass of sulfamethoxazole in the tablets, assuming that all of the sulfur present came from sulfamethoxazole?

g BaSO4 x (molar mass sulfa stuff/3*molar mass BaSO4)*100 = ?

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To find the percent by mass of sulfamethoxazole in the tablets, we need to determine the mass of sulfamethoxazole and the total mass of the tablets.

Step 1: Calculate the molar mass of sulfamethoxazole.
The molecular formula of sulfamethoxazole is C10H11N3O3S. We can find the molar mass by summing up the atomic masses of all the atoms in the formula:

Molar mass of C (10 atoms) = 10 * atomic mass of C
Molar mass of H (11 atoms) = 11 * atomic mass of H
Molar mass of N (3 atoms) = 3 * atomic mass of N
Molar mass of O (3 atoms) = 3 * atomic mass of O
Molar mass of S (1 atom) = atomic mass of S

Step 2: Calculate the mass of sulfamethoxazole.
Now that we have the molar mass of sulfamethoxazole, we can use it to calculate the mass of sulfamethoxazole in the tablets.

Given that 10.0 g of tablets containing sulfamethoxazole and trimethoprim were used, we assume all the sulfur present in the precipitated barium sulfate came from sulfamethoxazole.

Mass of sulfamethoxazole = (molar mass of sulfamethoxazole / molar mass of S) * mass of barium sulfate precipitate

Step 3: Calculate the percent by mass of sulfamethoxazole.
Finally, we can calculate the percent by mass of sulfamethoxazole by dividing the mass of sulfamethoxazole by the total mass of the tablets and multiplying by 100.

Percentage by mass of sulfamethoxazole = (mass of sulfamethoxazole / mass of tablets) * 100

Inputting the given information, we can calculate the values to find the final answer.