Answer:
4.10 x 10⁻⁸ M
Explanation:
The molarity (M) of a solution is defined as the number of moles of solute per liter of solution. We have to first calculate the number of moles of solute (benzene) from the mass and the molecular weight:
Benzene has the chemical formula C₆H₆. So, its molecular weight (MW) is calculated from the molar mass of C (12 g/mol) and H (1 g/mol):
MW(C₆H₆)= (12 g/mol x 6 C) + (1 g/mol x 6 H) = 78 g/mol
Then we convert the mass of benzene (0.32 mg) from mg to grams and divide the mass into the MW:
mass = 0.32 mg x 1 g/1000 mg = 3.2 x 10⁻⁴ g
moles of benzene = mass/MW = 3.2 x 10⁻⁴ g/(78 g/mol) = 4.10 x 10⁻⁶ mol
Now, we convert the volume of solution from dm³ to L:
liters of solution = 100 dm³ x 1 L/1 dm³ = 100 L
Finally, we divide the moles of benzene into the volume of solution in liters:
M = moles of benzene/liters of solution = 4.10 x 10⁻⁶ mol/100 L = 4.10 x 10⁻⁸ mol/L = 4.10 x 10⁻⁸ M
