Question

A liter of water was found to contain 10 mg of benzene (C6H6). What is the concentration of benzene in mg/L, ppm, and molarity?

Answer 1

The concentration of benzene is 10 mg/L or 10 ppm. To find molarity, we convert the mass of benzene to moles using its molar mass and then divide by the volume of the solution in liters. The molarity of the benzene is 1.28 x 10^-4 M.

Step-by-step explanation:

The concentration of benzene in the liter of water is 10 mg/L. This is because the question states that 10 mg of benzene is dissolved in one liter of water, and this is directly the concentration in mg per liter. To express this concentration in parts per million (ppm), we recall that 1 ppm is equivalent to 1 mg of substance per liter of water, since the density of water is approximately 1 g/mL, and there are 1000 g in a liter of water. Therefore, the concentration in ppm is also 10 ppm.

To calculate the molarity of benzene, we must first determine the molar mass of benzene, which is 78.11 g/mol (C6H6: 6 x 12.01 for carbon + 6 x 1.008 for hydrogen). The number of moles of benzene in 10 mg can be found using the formula: moles = mass (g) / molar mass (g/mol). Since we have 10 mg, we must first convert this to grams: 10 mg = 0.01 g. Thus, the number of moles of benzene is 0.01 g / 78.11 g/mol = 1.28 x 10-4 moles. Given that this is the amount in 1 liter, the molarity is 1.28 x 10-4 M.

Answer 2

10 mg/L: C₆H₆

10 ppm: C₆H₆

1.28×10⁻⁴ M : [C₆H₆]

Step-by-step explanation:

A liter of water was found to contain 10 mg of benzene (C6H6).

This can be understood as mg/L concentration. 10 mg of benzene are contained in 1L of solution.

If we want to write concentration of ppm, we assume μg/mL

So let's convert 10 mg to μg

10 mg . 1000 = 10000 μg

and 1L = 1000 mL

So μg/mL → 10000 μg / 1000 mL = 10

Molarity is mol/L

We know that the volume is 1L so let's convert the 10 mg of benzene to moles. (mass (g) / molar mass)

0.01 g / 78 g/mol = 1.28×10⁻⁴ moles