How To Prepare a Solution

Chemistry Quick Review of Solution Preparation

Volumetric flasks are used to accurately prepare solutions for chemistry.
Volumetric flasks are used to accurately prepare solutions for chemistry. COLIN CUTHBERT/SCIENCE PHOTO LIBRARY / Getty Images

Here's a quick overview of how to prepare a solution when the final concentration is expressed as M or molarity.

You prepare a solution by dissolving a known mass of solute (often a solid) into a specific amount of a solvent. One of the most common ways to express the concentration of the solution is M or molarity, which is moles of solute per liter of solution.

Example of How to Prepare a Solution

Prepare 1 liter of 1.00 M NaCl solution.

First calculate the molar mass of NaCl which is the mass of a mole of Na plus the mass of a mole of Cl or 22.99 + 35.45 = 58.44 g/mol

  1. Weigh out 58.44 g NaCl.
  2. Place the NaCl in a 1 liter volumetric flask.
  3. Add a small volume of distilled, deionized water to dissolve the salt.
  4. Fill the flask to the 1 L line.

If a different molarity is required, then multiply that number times the molar mass of NaCl. For example, if you wanted a 0.5 M solution, you would use 0.5 x 58.44 g/mol of NaCl in 1 L of solution or 29.22 g of NaCl.

Important Points to Remember

  • Molarity is expressed in terms of liter of solution, not liters of solvent. To prepare a solution, the flask is filled to the mark. In other words, it is incorrect to a 1 liter of water to a mass of sample to prepare a molar solution.
  • Sometimes it's necessary to adjust the pH of a solution. To do this, add enough water to dissolve the solute. Then add an acid or base solution dropwise (usually a hydrochloric acid or HCl solution for acid or sodium hydroxide or NaOH solution for a base) to reach the desired pH. Then add more water to reach the mark on the glassware. Adding more water won't change the pH value.
    Format
    mla apa chicago
    Your Citation
    Helmenstine, Anne Marie, Ph.D. "How To Prepare a Solution." ThoughtCo, Oct. 9, 2017, thoughtco.com/how-to-prepare-a-solution-606091. Helmenstine, Anne Marie, Ph.D. (2017, October 9). How To Prepare a Solution. Retrieved from https://www.thoughtco.com/how-to-prepare-a-solution-606091 Helmenstine, Anne Marie, Ph.D. "How To Prepare a Solution." ThoughtCo. https://www.thoughtco.com/how-to-prepare-a-solution-606091 (accessed November 22, 2017).