chemist at work, chemistry set, mixtures and solutions, using a concentration formula

How to Calculate Concentrations of Solutions and Mixtures

Read Time: 5 minutes

Chemistry might seem like a complicated branch of science, but most of the research in this field looks at mixing different things together and seeing what happens next. One thing chemists do is create solutions and mixtures to carry out their experiments. What are solutions? What are mixtures? How do chemists use each concentration formula, and can you replicate the process at home?

Let’s take a closer look at these questions and see what we can learn about this basic tenant of chemistry.

What Are Solutions?

When you mix a spoonful of sugar in a glass of warm water, what happens? Spin the spoon a few times, and the sugar dissolves in the water, creating something sweet to sip. Congratulations — you’ve made your first solution. What are other examples of solutions?

Chemists define solutions as any mixture of two or more substances where they become homogenous — or completely mixed — and can’t be separated by mechanical means. For instance, you can’t get sugar out of your sugar-water by running it through a screen or a filter. Solutions are two parts — the solvent and the solute. In our sugar-water example, the water is the solvent, and the sugar is the solute.

Solutions aren’t limited to the chemistry lab, though. There are plenty you might find lying around your house. For instance, soda and other carbonated beverages are fizzy because of carbon dioxide dissolved in the liquid. Household bleach is a solution of water, the solvent, and sodium hypochlorite, the solute.

Your morning cup of coffee is a solution created when coffee grounds or particles completely dissolve in water. Test this idea out by diluting your coffee with water — the mixture will look clear, not cloudy. The mayo you spread on sandwiches is also a solution known as an emulsion. It’s a homogenous mixture of eggs and oil where both the solvent and the solute are liquid.

Now that you have a basic idea of what a solution is let’s move on to the next character in our story — the mixture.

What Are Mixtures?

Remember how you can’t separate solutions by mechanical means? Mixtures are the exact opposite. They’re two different materials, but they don’t become homogenous, so you can separate them by filtering or screening.

Anything you mix that you can separate again is considered a mixture. When it comes to examples of mixtures, consider the simple idea of rocks in a jar of water. The properties of the stones and the water remain the same, and you can remove the rocks and filter out any small particles that might remain.

Where might you find other mixtures in your household? Look in your fridge for any vinaigrette-style salad dressing. The oil and vinegar mix if shaken to create a tasty salad dressing. However, if you leave them to sit for a while, the two components will separate. Speaking of salads, an assortment of different vegetables is a mixture.

Have some mud in your yard? You’ve got a mixture of water and dirt. The two appear homogenous, but neither is changed by the other. If you experience a heatwave, the water dries up, and the mud goes back to being dirt. The smoke floating up from barbeque is also a mixture of solid particles released from the fire.

Now that you have a good idea of what both solutions and mixtures are, how can you calculate the concentration of each?

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Concentration Formulas to Keep in Mind

There are a few ways to calculate the concentration of a solution. The first step is to identify what the solvent and solute are in the solution. For this example, we’ll head back to that sugar-water analogy used earlier, where our solvent is water, and our solute is sugar. Now we’ve got a few different concentration formulas to choose from:

  1. Parts per million/billion (ppm/ppb): This calculation only applies to very diluted solutions. If you had 1 million parts of water and 50 parts of it were sugar, you’d have a measurement of 50 ppm.
  2. Grams per liter (g/L): A simple measurement perfect for at-home chemists. If you’ve got 50 grams of sugar and 1 liter of water, your result would be 50 g/L.
  3. Percent composition by mass: For this calculation, divide the mass of the solute — the sugar in this case — by the mass of the solvent. If your entire solution weighs 100 grams and you added 50 grams of sugar, you have a 50% sugar solution.
  4. Volume percent: For this formula, divide the volume of the solution by the volume of the solute and multiply it by 100%. Alcoholic drinks are an excellent example of this, as the labels have a percentage of ethanol — maybe 12 to 15%. That means there are 12 to 15 ml of ethanol for every 100 ml of the liquid.

When you’re looking at solutions, there is also the concept of mole, molarity and molality. Moles are individual bits of the solute, and molarity is the number of moles in a solution. To discover the molar mass of a solute, you need to know the molar mass of each element in the solute. This is something you can often find on the periodic table.

Calculating the Concentration of Mixtures

Calculating the concentration of mixtures rather than homogenous solutions is simple in cases where you can separate the solute from the solvent. If you’ve got a mixture of rocks and water, filter out the stones and measure each component on its own.

If you’re mixing liquids, such as oil and vinegar, you can use the volume percent mixture mentioned above. Most vinaigrettes are one part vinegar to two parts oil, as well as other additional ingredients to add flavor.

If your components aren’t easy to separate, use the molar concentration method. The steps are nearly identical for calculating the concentration of a mixture as they are for calculating the concentration of a solution.

Your Future in Chemistry

When it comes to chemistry, mixtures and solutions are an integral part of the science — but that doesn’t mean they’re limited to the lab. Take a look in your kitchen or your household. What other solutions and mixtures can you discover?

If you want a future in chemistry, knowing how to use each concentration formula is crucial. You can use your knowledge to excel in several branches of the science, such as inorganic chemistry. Before you know it, you’ll be able to take on experts like William Lipscomb, who won the Nobel Prize in Chemistry in 2976 for his study of boranes with x-ray techniques.

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Article by: Megan Ray Nichols

Megan Ray Nichols is a freelance science writer and science enthusiast. Her favorite subjects include astronomy and the environment. Megan is also a regular contributor to The Naked Scientists, Thomas Insights, and Real Clear Science. When she isn't writing, Megan loves watching movies, hiking, and stargazing.