How to Make Solutions for Chemistry and Biology Experiments
Solutions
Solutions
Solutions are used in a wide range of science experiments including chemistry, biology, health, cooking, and materials science. This video and written tutorial will guide you through how to make solutions and how to calculate the concentration of a solution.
If you have a solution and need information on how to dilute it, or how to make serial dilutions of a sample, check out our guide on How to Make Dilutions and Serial Dilutions.
Solution
What is a solution?
A solution is a mixture made by dissolving one or more substances in a liquid. In a solution, the substance that is being dissolved is the solute and the liquid it is being dissolved in is the solvent. For example, when making lemonade the solutes (substances being dissolved) are sugar and lemon juice, and the solvent (liquid they are dissolved in) is water. Notice that the solutes can be either liquids or solids in a solution.
Solutions must be homogeneous. Homogenous means "the same throughout". Going back to our lemonade example, you would not expect a glass of lemonade to taste different with each sip. One sip should not be sweeter or more sour than the next. Instead, each sip should taste the same. For that to be true, the solutes must dissolve and mix completely with the solvent. A mixture of sand and water is not a solution because the sand does not dissolve in the water.
It is less common, but solutions can also be made of gases. A gas dissolved in a liquid is a solution. A gas mixed homogeneously with another gas is also a solution, but it is often called a gas mixture instead.
How to make a solution
There are seven steps to making a solution.
- Decide on the solution's concentration. The concentration describes how much solute is in the solution. For example, a 10% weight by volume saline solution contains 10 grams (g) of salt in 100 milliliters (mL) of water. There are many ways of expressing the concentration of a solution. Many science experiments call for a specific solution concentration. If you are making your own experimental procedure, you will need to decide on the concentration yourself based on your background research.
- Calculate the solute and solvent needed. Once you know the desired concentration of the solution and how much solution is needed, you can calculate the amount of solute and solvent needed. See the How to Calculate Solution Concentrations section for help with the math.
- Take safety precautions. If you are using hazardous materials or need to keep your solutions sterile (germ-free), you may need to use some safety equipment. The most common safety equipment for making solutions in student science projects are:
- Latex or nitrile gloves: used to keep germs from your hands out of your solutions and most chemicals off of your skin. If you are using harsh chemicals, like a very strong acid or base, you may need to use chemical-resistant gloves. This is not common for most science projects.
- Chemical splash goggles or glasses: used to keep chemicals from getting in your eyes. If the chemicals you are using may irritate your eyes, these are a good idea.
- Weigh or measure the solute.
- If the solute is a solid, use a scale to weigh out the correct amount. Use a scale that measures to at least a tenth of a gram (0.1 g) to be accurate.
- If the solute is a liquid, use a measuring cup, graduated cylinder, or pipette to measure out the correct amount. Which you use will depend on the type of science project. A cooking science project may use a measuring cup. A chemistry project is likely to use a graduated cylinder or pipette for more accuracy.
- Dissolve the solute. For the most accuracy, pour the solute into a graduated cylinder or measuring container large enough to hold all of the solution. Add less than the total amount of solvent. Mix the solvent and solute until the solute has dissolved completely. Add more solvent until the solution is at the desired volume. Mix again. This technique is shown in the How to Make a Solution video.
- Do safety and quality checks. Sometimes a solution needs to have specific properties. If necessary, check the pH, conductivity, or other properties of your solution. Based on the results, adjust your solution as needed.
- Label and store the solution. If needed, transfer your solution to a storage container. Immediately label the container with the name of the solution, the concentration, and the date it was made.
Express Concentration
How to express the concentration of a solution
There are many ways to express the concentration of a solution. Here are a few common ones.
- Mass/Volume Percentage (%m/v) is the percentage of the mass of the solute in grams per 100 mL of solution. It is calculated using the formula:
For example, if you dissolve 10 grams of solute in 100 mL of solution the mass/volume percentage is 10%.
This is often used for making solutions where the solute is a solid. Sometimes this is called the weight/volume percentage (%w/v).
- Volume/Volume Percentage (%v/v) is the percentage of the volume of the solute in milliliters per 100 mL of solution. It is calculated using the formula:
For example, if you dissolve 20 mL of solute in 80 mL of solution, the volume/volume percentage is 25%.
This is commonly used for making solutions where the solute is a liquid.
- Molarity (M) is the number of moles of solute dissolved per liter of solution (mol/L). It is calculated using the formula:
For example, if you dissolve 0.5 moles of solute in 1 liter of solution, the molarity is 0.5M.
This is often used for standard solutions found in chemistry and biology laboratories.
- Mole fraction (Χ) is the relative number of moles of the substance you are interested in compared to the total number of moles in the solution. If you made a solution from two substances, A and B, the mole fraction for substance A would be calculated as:
For example, if you make a solution with 0.5 moles of substance A and 1.5 moles of substance B, the mole fraction of substance A (XA) is 0.25 and the mole fraction of substance B (XB) is 0.75.
Mole fraction is often used when talking about gas solutions.
Calculate
How to calculate solution concentrations
When making calculations about solutions, there are three important pieces of information:
- The amount of solute (described in mass, volume, or moles).
- The total amount of the solution (described in volume or moles)
- The concentration of the solution (described by a concentration expression)
If you know two out of three of those pieces of information, you can use algebra to calculate the third.
This table shows you what you can calculate based on what you already know.
| Amount of solute | Total amount of solution | Concentration of solution |
|---|---|---|
| known | known | calculate |
| known | calculate | known |
| calculate | known | known |
The How to Make a Solution video shows you a few example calculations. For more examples and an in-depth explanation of the algebra involved, watch this video:
Learn
Learn about solutions with these hands-on science projects
Hands-on science projects are a great way to learn more about how to make solutions, use solutions, and the properties of different solutions. Try some of these!
- A Soluble Separation Solution
- Saturated Solutions: Measuring Solubility
- Bubble-ology
- When Science is Sweet: Growing Rock Candy Crystals
- Excess Volume: Investigate the "Shrinking Liquids" Effect
- Explore the Mixing Behavior of Liquids
- Measuring Sugar Content of a Liquid with a Laser Pointer
