Question

0.000333 g fluorescein (332.32 g/mol) is dissolved in 225 mL solution of ethanol. The density of ethanol is 0.785 g/mL.

What is the concentration of the solution in molarity (M)?
How many ppm? I already know that the molarity is 4.45E-6. I just need help on trying to find the ppm please.

Answer 1

`4.45* 10^(-6) M` is the concentration of the solution in molarity.

The concentration of fluorescein in solution is 1.88 ppm.

Step-by-step explanation:

`Molarity=(Moles)/(Volume(L))`

Moles of fluorescein =
`(0.000333 g)/(332.32 g/mol)=1.002* 10^(-6) mol`

Volume of the fluorescien ethanol solution = 225 mL = 0.225 L

1 mL = 0.001 L

Molarity of the solution :

`(1.002* 10^(-6) mol)/(0.225 L)=4.45* 10^(-6) M`

`4.45* 10^(-6) M` is the concentration of the solution in molarity.

`\text{ppm}=\frac{\text{Mass of solute}}{\text{Mass of solution}}* 10^6`

Both the masses are in grams.

Mass of solute that is flouroscein = 0.000333 g

Mass of ethanol = m

Density of the ethanol = d = 0.785 g/mL

Volume of the ethanol = 225 mL

`m=0.785 g/mL* 225 mL=176.625 g\approx 177 g`

Mass of solution = 0.000333 g + 177 g = 177.000333 g

Concentration in ppm:

`(0.000333 g)/(177.000333 g)* 10^6=1.88`

The concentration of fluorescein in solution is 1.88 ppm.

Answer 2

Parts per million of a solution is the mass fraction. It denotes the amount of one substance in one million parts of the other. Now, we can calculate the mass of the ethanol solution using its density and volume.
mass = density x volume
= 0.785 x 225
= 176.625 g
0.000333 : 176.625 = x : 1,000,000
x = (0.000333/176.625) * 1000000
x = 1.89 parts per million