There are many ways to prepare simple chemical solutions. You can even do it at home or at work. Regardless of whether you are making a solution from a powdered compound or by diluting a liquid solution, it is not difficult to determine the correct amounts of each compound and solution to use. Remember that every time you go to work with chemical solutions it is necessary to use safety equipment to avoid injuries.
Method 1 of 4: Use a Formula Based on Weight or Volume
Step 1. Define a solution through percentage by weight or volume.
A percent solution simply means parts percent. In terms of preparing a chemical solution, this means that you will have 1 gram of compound for every 100 milliliters of liquid, or 1 mL / 100 mL if you are working with a compound that is already in a liquid state.
- Example of solution by weight: A 10% solution by weight simply means that you have 10 grams of compound dissolved in a 100 mL solution.
- Example of solution by volume: A 23% solution by volume simply means that you have 23 mL of liquid compound per 100 mL of solution.
Step 2. Identify the bulk solution you are going to prepare
In order to determine the required mass of the compound, you must first determine the final volume of the solution you want to make. The volume will be determined by the amount of solution you need for the task, how often you need it, and the stability of the solution over time.
- If the solution must be fresh (just made) each time you use it, make only the amount you need.
- If it's a long-term stable solution, you can prepare a larger volume to store for later use.
- For example: create a 5% solution of NaCl in 500 mL of water.
Step 3. Calculate the number of grams needed to prepare the solution
To calculate the number of grams needed to make the percentage solution, you have to multiply using the formula: number of grams = (desired percentage) (desired volume / 100 mL). The desired percentage must be expressed in grams and the desired volume must be expressed in milliliters.
- For example: create a 5% solution of NaCl in 500 mL of water.
- Number of grams = (5g) (500 mL / 100 mL) = 25 grams.
- If the NaCl was already dissolved in a liquid, you should add 25 mL of NaCl instead of grams of powder and subtract that volume from the final volume: 25 mL of NaCl in 475 mL of water.
Step 4. Weigh the mass of the compound
Once you have calculated your desired mass, you will need to weigh it. Using a calibrated scale, place a weighing pan and zero the scale. Weigh out the required amount of compound in grams and set it aside.
- Always clean up any remaining powder on the balance before continuing to prepare the solution.
- For example: it weighs 25 g of NaCl.
Step 5. Dilute the compound in the required amount of solvent
Unless otherwise stated, the compound will most likely need to be dissolved in water. Using a measuring cylinder (graduated cylinder specially designed for measuring volume), measure the desired amount of liquid. Next, mix the liquid with the powdered compound until it dissolves.
- Label the container clearly indicating both the chemical and the concentration.
- For example: mix 500 mL of water and 25 g of NaCl to obtain a 5% solution.
- Remember that if you are going to dilute a liquid compound, you must subtract the volume of the liquid you add from the final volume: 500 mL - 25 mL = 475 mL of water.
Method 2 of 4: Prepare a Molar Solution
Step 1. Identify the Formula Weight (FP) of the component you are going to use
The formula weight (often used interchangeably with "molecular weight") of a compound is expressed in grams / mole (g / mole) on chemical bottle labels. If you can't find the formula weight on the bottle, you can search for the compound online to find out.
- The formula weight of a compound is the mass in grams of one mole of that compound.
- For example: the formula weight of sodium chloride (NaCl) is 58.44 g / mol.
Step 2. Define in liters the volume of the solution you are going to prepare
It is very easy to make a one liter solution since the molarity is simply moles / liter. However, you may need to prepare more than a liter, or less, depending on how you intend to use the solution. You will use the final volume of the solution to calculate the number of grams needed to prepare the molar solution.
- For example: prepare a 50 mL solution of 0.75 molar NaCl.
- To convert mL to L, divide by 1000: 0.05 L.
Step 3. Calculate the number of grams needed to make the desired molar solution
To calculate the necessary number of grams you must use the equation number of grams = (desired volume) (desired molarity) (formula weight). Remember that the desired volume must be expressed in liters, the molarity in moles per liter and the formula weight in grams per mole.
- For example: if you want to make 50 mL of 0.75 molar NaCl solution (MP: 58.44 g / mol), you can calculate the required number of grams of NaCl.
- Number of grams = 0.05 L * 0.75 mol / L * 58.44 g / mol = 2.19 grams of NaCl.
- When canceling all units, only the grams of compound should remain.
Step 4. Weigh the mass of the compound
Using a properly calibrated scale, weigh the necessary mass for the compound. Before weighing, place a weighing pan on the scale and set it to zero. Add compound to the plate until you get the right amount.
- Clean the scale when you are done using it.
- For example: it weighs 2.19 grams of NaCl.
Step 5. Dilute the powder in the corresponding volume of liquid
Most solutions are diluted with water unless otherwise noted. The volume of the liquid to use is the same that you used to calculate the mass of the compound. Mix the compound and water until the powder is completely dissolved.
- Label the solution clearly indicating the molarity and compound so that it can be easily identified in the future.
- For example: using a measuring cylinder (graduated cylinder to measure volume), measure 50 mL of water and mix it with the 2.19 g of NaCl.
- Continue mixing until the powder dissolves completely.
Method 3 of 4: Dilute Solutions of Known Concentrations
Step 1. Define the concentration of each solution
When you dilute a solution, you must know the concentration of the initial solution and the final concentration you need the solution to have. This method is used to dilute highly concentrated solutions into less concentrated solutions.
For example: make 75 mL of 1.5 M NaCl solution from a 5 M starting solution. The starting solution has a concentration of 5 M and you want to dilute it to a final concentration of 1.5 M
Step 2. Determine the volume of the solution you are going to prepare
It is necessary to define the total volume of the solution that you are going to prepare. You have to calculate the amount of solution to add to dilute it and reach the concentration and volume you are looking for.
For example: make 75 mL of 1.5 M NaCl solution from a 5 M starting solution. In this example, you need the final solution to have a volume of 75 mL
Step 3. Calculate the volume of the initial solution to add to the final solution
To determine the amount of starting solution to dilute, use formula V1C1= V2C2, where V1 is the volume of the initial solution and C1 is the concentration of the initial solution; V2 is the desired final volume and C2 is the desired final concentration of the solution.
- To calculate the volume of initial solution needed, you must rearrange the equation as follows: V1: V1 = (V2C2) / C1
- For example: make 75 mL of 1.5 M NaCl solution from a 5 M starting solution.
- V1 = (V2C2) / C1 = (0.075L * 1.5M) / 5M = 0.0225L.
- Convert the L back to mL by multiplying by 1000: 22.5 mL.
Step 4. Subtract the volume of the starting solution from the desired final volume
When diluting the starting solution, you need to make sure that the final solution is the desired volume. To make the dilution correctly you must subtract the volume of the initial solution from the final volume.
For example: you want to obtain a final volume of 75 mL and you are going to add 22.5 mL of your initial solution. Therefore, 75 - 22.5 = 52.5 mL. This volume is the amount of dilution solution you should use
Step 5. Combine the volume of starting solution you calculated with the volume of dilution solution
Using a measuring cylinder (graduated cylinder specially designed for measuring volume), measure the volume of the starting solution and then mix that amount with the required volume of dilution solution.
- For example: measure 22.5 mL of 5 M NaCl starting solution and dilute it in 52.5 mL of water. Begin to mix.
- Label the container indicating both the concentration and the compound: 1.5 M NaCl.
- Remember that when you dilute an acid in water, you must always add the acid to the water.
Method 4 of 4: Take Necessary Safety Precautions
Step 1. Put on your personal protective equipment (or "PPE")
If you are going to work with strong chemicals and solutions, you better make sure your body is safe from danger. To handle these types of components it is essential to have a lab coat, closed shoes, eye protection and gloves.
- Put on a lab coat made of some flame retardant material.
- Eye protection should have side shields that protect you from splashes on your face.
Step 2. Work in an area with good ventilation
When you mix solutions, volatile gases can be produced that escape into the air. Some chemicals should only be handled using a fume hood like those found in labs. If you are going to work at home, open the windows and turn on the fan to make sure the air circulates.
Step 3. Acids are added to the water
When dissolving strong acids, you should always add them to the water (and not the other way around). When water mixes with an acid, the reaction is exothermic (it releases heat) and it can be explosive if you pour the water into the acid instead of pouring the acid into the water.
Remember the precautions you must take every time you work with acids
- It would be good if you read a little before starting. Knowledge is power.
- Try using common household chemicals. Don't do anything too difficult. If you think the result could be dangerous, it probably is!
- Never mix bleach with ammonia.
- Put on safety gear, goggles, a plastic apron, and neoprene gloves if necessary.