A reference solution is to be prepared with 5 PPM parabenzopyrene (molecular weight = 252). The quantity of parabenzopyrene required for preparing one litre 5 PPM solution is
(A) 252 mg (B) 25.2 mg (C) 5 mg (D) 252 g
You want 5 ppm. Remembering that 1 ppm is 1 mg/L, you want 5 mg/L.
So if you want 5 ppm that is 5 mg/L; you want 1 L which means you want 5 mg. Right?
5 mg
To determine the quantity of parabenzopyrene required for preparing a 5 PPM (parts per million) solution, we need to follow these steps:
Step 1: Convert the desired concentration from PPM to a mass fraction.
PPM is a unit that expresses the ratio of the number of parts of the solute to one million parts of the solution. In this case, we want a 5 PPM solution, which means there are 5 parts of parabenzopyrene in one million parts of the solution.
To convert PPM to a mass fraction, we divide the PPM value by 1 million:
5 PPM / 1,000,000 = 0.000005 mass fraction
Step 2: Calculate the mass of parabenzopyrene needed.
To determine the mass of parabenzopyrene required for one liter of solution, we multiply the mass fraction by the total volume of the solution:
0.000005 x 1000 mL = 0.005 grams
Finally, we convert grams to milligrams (since the options given are in milligrams):
0.005 grams x 1000 = 5 mg
Therefore, the correct answer is (C) 5 mg.
To prepare a 5 PPM (parts per million) solution with parabenzopyrene, the first step is to understand the definition of parts per million.
PPM is a measurement unit that represents the concentration of a substance in a solution. It is calculated by dividing the amount of solute (in this case, parabenzopyrene) by the total volume and then multiplying by one million.
Now, let's break down the calculation step-by-step:
Step 1: Convert 5 PPM to a decimal
To convert 5 PPM to a decimal, we divide it by one million:
5 PPM / 1,000,000 = 0.000005
Step 2: Calculate the quantity of parabenzopyrene needed
To calculate the quantity of parabenzopyrene needed, we multiply the decimal value obtained in step 1 by the total volume of the solution (one liter). Since the concentration is given in PPM, the quantity will be in grams.
0.000005 * 1000 (conversion from liters to milliliters) = 0.005 grams
However, the molecular weight of parabenzopyrene is given as 252 grams per mole. To convert from grams to moles, we divide the quantity by the molecular weight:
0.005 grams / 252 grams per mole = 0.00002 moles
Finally, to convert from moles to the desired unit of measurement (micrograms), we use the molecular weight and Avogadro's number (6.022 x 10^23 molecules per mole):
0.00002 moles * 252 grams per mole * 10^6 micrograms per gram = 5.04 micrograms
So, the correct option is (D) 252 µg.