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# Solution Preparation Guide

Carolina offers many types of premade solutions, but some teachers prefer to make their own. If that is your interest, keep reading. This brief guide will provide you with the information you need to make a number of solutions commonly used in educational laboratories. However, let’s review some safety considerations before we discuss preparing solutions.

First, always wear appropriate personal protective equipment (PPE) when handling chemicals and preparing solutions. Next, read a chemical’s label twice before use. Read it when you take the chemical off the shelf and again before you remove any chemical from the bottle. Finally, when using concentrated chemicals to prepare solutions, be sure you slowly add the more concentrated solution to the less concentrated one. The reverse procedure can cause the solution to boil and spatter. For more information on lab safety, visit Carolinachemistry.com.

### Solution Preparation

#### Molar solutions

Molarity (M) means the number of moles of solute per liter of solution. To prepare a 1 M solution, slowly add 1 g formula weight of compound to a clean 1-L volumetric flask half filled with distilled or deionized water. Allow the compound to dissolve completely, swirling the flask gently if necessary. Once the solute is completely dissolved and the solution is at room temperature, dilute to the mark with water. Invert the flask several times to mix. Here are a couple of examples of how to use this method:

• To make a 1 M solution of sodium hydroxide, slowly add 40 g sodium hydroxide to 500 mL distilled or deionized water in a 1-L volumetric flask. When the solids are completely dissolved and the solution is at room temperature, dilute to the mark and invert the flask several times to mix.
• To make a 1 M solution of acetic acid, dissolve 60.05 g acetic acid in 500 mL distilled or deionized water in a 1-L volumetric flask. Because acetic acid is a liquid, the acid may also be measured by volume. Divide the mass of acid by its density (1.049 g/mL) to determine the volume (57.24 mL). Use either 60.05 g or 57.24 mL acetic acid to make the solution. Swirl the flask gently to mix the solution. When the solution is at room temperature, dilute to the mark and invert the flask several times to mix.

#### Dilutions

When preparing a dilution, decide the volume and molar concentration of the resulting solution you require. Use the following equation to determine how much of the concentrated reagent is needed to prepare the diluted solution,

Mreagent × Vreagent = Mdilution × Vdilution

where M is molarity and V is volume.

Slowly add the calculated volume of concentrated reagent to the proper-size volumetric flask half filled with distilled or deionized water and swirl the flask to mix. Once the solution is at room temperature, dilute to the mark with water and invert the flask several times to mix.

For example, what volume of 10 M acetic acid is required to prepare 1.0 L of 0.50 M acetic acid?

10 M × Vreagent = 0.50 M × 1.0 L
Vreagent = 0.050 L = 50 mL

A volume of 50 mL of 10 M acetic acid is required to prepare 1.0 L of 0.50 M acetic acid.

#### ChemCapsules

ChemCapsules are an alternative to preparing common solutions from bulk chemicals. Each capsule contains the necessary amount of chemical needed to make a standard solution. To prepare the solution, place the capsule in the correct amount of water. The capsule dissolves, releasing the chemical into the water. Mix and you have a solution ready to use.

For example, the Bromthymol Blue ChemCapsule contains 0.04 g of bromthymol blue. When dissolved in 100 mL of distilled water, it creates a standard 0.04% bromthymol blue solution. There is no spatula to clean, no weigh boat to discard, and no leftover bromthymol blue.

Compared to preparing solutions from bulk chemicals, ChemCapsules:

• Save money—you buy only the amount of chemical you need
• Save time—you don’t have to weigh the chemical
• Save storage space—ChemCapsules take up less space than bulk chemicals
• Reduce error—ChemCapsules provide the right amount of chemical each time

Carolina offers over 40 ChemCapsules. To see them, visit Carolinachemistry.com. Try ChemCapsules and experience the benefits.

### Recipes for common solutions

To prepare these solutions, slowly add the necessary ingredients to a 1-L volumetric flask half filled with distilled or deionized water. Allow the ingredients to dissolve completely, swirling the flask gently if necessary. Once the solute is completely dissolved and the solution is at room temperature, dilute to the mark with water. Invert the flask several times to mix.

Each reagent in the following chart is linked to our online catalog for additional information and convenient purchase. For the liquids, we have referenced the 500-mL size of the reagent- or ACS-grade chemical packaged in a plastic-coated safety bottle. For sodium hydroxide, we have listed the 500-g size of the reagent-grade chemical. Other sizes and grades may be available. Please consult our catalogs for more information.

 Solution Quantity to Add to 1 L Water Final Concentration Acetic acid, glacial (17.4 M) 5.7 mL acetic acid 0.1 M 57 mL acetic acid 1 M Hydrochloric acid (12.1 M) 8.3 mL hydrochloric acid 0.1 M 83 mL hydrochloric acid 1 M 248 mL hydrochloric acid 3 M 496 mL hydrochloric acid 6 M Sodium hydroxide 4 g sodium hydroxide 0.1 M 40 g sodium hydroxide 1 M Sulfuric acid (18.1 M) 56 mL sulfuric acid 1 M

Whether you decide to make your own solutions or buy them from us premade, you’ll find everything you need at Carolina. Check out our CarolinaChemistry and CarolinaScience catalogs, or visit us at Carolinachemistry.com. We hope you find this brief guide useful and encourage you to download Carolina’s Solution Preparation Manual for further study. Also, check out this video demonstration of solution preparation. Work safely and have fun preparing solutions!

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