A sample of 0.6760 g of an unknown compound containing barium ions (Ba2+) is dissolved in water and treated with an excess of Na2SO4. If the mass of the BaSO4 precipitate formed is 0.1405 g, what is the percent by mass of Ba in the original unknown compound?
Ba^+2 + SO4^= -->BaSO4.
moles BaSO4 = g/molar mass = ??
moles Ba is the same as moles BaSO4.
g Ba = moles Ba x atomic mass Ba.
%Ba = (g Ba/mass original sample)*100 =??
3.45
To find the percent by mass of Ba in the original unknown compound, you need to determine the mass of Ba in the BaSO4 precipitate and then calculate it as a percentage of the mass of the original compound.
To calculate the mass of Ba in the BaSO4 precipitate, you first need to know the molar mass of BaSO4. The molar mass of BaSO4 is calculated by adding up the atomic masses of its constituent elements: Ba (barium), S (sulfur), and O (oxygen). The atomic masses can be found on the periodic table.
The atomic mass of Ba is 137.33 g/mol, the atomic mass of S is 32.06 g/mol, and the atomic mass of O is 16.00 g/mol. Therefore, the molar mass of BaSO4 is:
Molar mass of BaSO4 = (1 × Ba) + (1 × S) + (4 × O)
Molar mass of BaSO4 = (1 × 137.33) + (1 × 32.06) + (4 × 16.00)
Molar mass of BaSO4 = 233.39 g/mol
Now that you know the molar mass of BaSO4, you can calculate the number of moles of BaSO4 that corresponds to the mass of the BaSO4 precipitate. To do this, divide the mass of the BaSO4 precipitate by its molar mass:
Number of moles of BaSO4 = Mass of BaSO4 / Molar mass of BaSO4
Number of moles of BaSO4 = 0.1405 g / 233.39 g/mol
Now, use stoichiometry to determine the number of moles of Ba in these moles of BaSO4. The balanced chemical equation for the reaction between Ba2+ and SO42- is:
Ba2+ + SO42- -> BaSO4
From the balanced equation, you can see that one mole of BaSO4 contains one mole of Ba2+. Therefore, the number of moles of Ba is equal to the number of moles of BaSO4:
Number of moles of Ba = Number of moles of BaSO4
Finally, calculate the percent by mass of Ba in the original unknown compound. To do this, divide the mass of Ba by the mass of the original unknown compound and multiply by 100:
Percent by mass of Ba = (Mass of Ba / Mass of original unknown compound) × 100
In this case, the mass of the original unknown compound is given as 0.6760 g.
Using these calculations, you can find the percent by mass of Ba in the original unknown compound.