Molarity, a measure of the concentration of a substance in a solution, can be derived from parts per million (ppm), a common unit for expressing the proportion of a substance present in a mixture. To convert ppm to molarity, an understanding of the relationship between ppm, mass, moles, and volume is crucial. This conversion involves calculating the mass of the substance, converting mass to moles, and finally determining the molarity by dividing the number of moles by the volume of the solution.
Converting Parts Per Million (ppm) to Molarity (M)
Converting parts per million (ppm) to molarity (M) is a common task in chemistry. Here’s a step-by-step guide to help you understand the process:
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Determine the molecular weight of the solute: The first step is to find the molecular weight of the substance you’re converting. This is the sum of the atomic weights of all the atoms in the molecule. You can find molecular weights in reference tables or online databases.
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Convert ppm to mg/L: ppm is a measure of concentration that represents the mass of a substance in parts per million per unit of volume. To convert ppm to mg/L, multiply the ppm value by the molecular weight of the solute and then divide by 1,000,000.
mg/L = ppm * Molecular weight / 1,000,000
- Convert mg/L to moles/L (molarity): To convert mg/L to moles/L, divide the mg/L value by the molecular weight of the solute in grams per mole.
Molarity (M) = mg/L / Molecular weight in g/mol
Example:
Suppose you have a solution with a concentration of 10 ppm of NaCl. The molecular weight of NaCl is 58.44 g/mol.
- Convert ppm to mg/L:
mg/L = 10 ppm * 58.44 g/mol / 1,000,000 = 0.5844 mg/L
- Convert mg/L to molarity:
Molarity = 0.5844 mg/L / 58.44 g/mol = 0.01 M
Table Summarizing the Conversion Steps:
| Step | Formula |
|---|---|
| Convert ppm to mg/L | mg/L = ppm * Molecular weight / 1,000,000 |
| Convert mg/L to molarity | Molarity = mg/L / Molecular weight in g/mol |
Question 1:
How do you convert parts per million (ppm) to molarity (M)?
Answer:
To convert ppm to M, divide the ppm value by the molecular weight of the substance and the volume of the solution in liters.
Question 2:
What is the molarity of a solution that contains 100 ppm of sodium chloride (MW = 58.44 g/mol) in 1 liter of water?
Answer:
Molarity = (100 ppm / 58.44 g/mol) * 1 L = 0.00171 M
Question 3:
How many moles of calcium carbonate (MW = 100.09 g/mol) are present in a 200 ppm solution with a volume of 500 mL?
Answer:
Moles = (200 ppm / 100.09 g/mol) * 0.5 L = 9.99 x 10^-4 moles
And that’s it, folks! You’re now equipped with the knowledge to effortlessly convert between parts per million and molarity. Remember, it’s all about ratios and proportions. If you ever need a refresher, don’t hesitate to drop by again. We’re always here to help. Until next time, keep converting those units with ease!