Name: molarity and dilution in solutions
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 59 s
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K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.6.1

Solution Concentration and Dilution

In a given quantity of solvent, different amounts of solutes can be added to create solutions of varying concentrations. 

In a dilute solution, the proportion of solute relative to the solvent is small, whereas for a concentrated solution, the proportion is large.

The concentration of a solution is expressed as molarity, which is the number of moles of solute per liter of solution. 

The denominator is the volume of the solution and not the volume of the solvent. Therefore, to make 1 liter of a 1-molar solution, 1 mole of solute is added to a volumetric flask, which is then filled to the 1-liter demarcation with the solvent. Similarly, if 1 mole of solute is added to another flask and then filled to the 0.5 liter mark with solvent, this would give a 2-molar solution.

The molarity of the solution can be used as a conversion factor between the moles of the solute and the volume of the solution. 

Suppose 237 grams of potassium permanganate is dissolved in water to make a 3-molar solution. To calculate the total volume of the solution, first, the mass of the solute is converted to moles. Then, the number of moles is divided by the molarity to get a volume of 0.5 liters.

If more water is ad

solution concentration and dilution

The relative amount of a given solution component is known as its concentration. Often, though not always, a solution contains one component with a concentration that is significantly greater than that of all other components. This component is called the solvent and may be viewed as the medium in which the other components are dispersed or dissolved. Solutions in which water is the solvent are, of course, very common on our planet. A solution in which water is the solvent is called an aqueous solution.

A solute is a component of a solution that is typically present at a much lower concentration than the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).

Concentrations may be quantitatively assessed using a wide variety of measurement units, each convenient for particular applications. Molarity (M) is a useful concentration unit for many applications in chemistry. Molarity is defined as the number of moles of solute in exactly 1 liter (1 L) of the solution and has the units of &#8216;mol/L&#8217;.

<img alt="Molarity formula: M = moles of solute/volume in liters, chemistry concept, educational diagram." src="/files/core/CDNSource/lessons/1021/1021_Equations-01.png" style="height: 40px;" data-altupdatedat="1761830439000" data-alt="Eq1" />

Note that in the molarity equation, the volume of solution, and not the volume of solvent, is used. This is because, depending on the nature of interactions between the solute and solvent, the solute can change the volume of the solution. Hence, in the molarity equation, we use the total solution volume (i.e., solvent volume + solute volume). Because solution volumes vary with temperature, molar concentrations will likewise vary. When expressed as molarity, the concentration of a solution with identical numbers of solute and solvent species will be different at different temperatures, due to the contraction/expansion of the solution.

<h4>Dilution of Solutions</h4>

Dilution is the process whereby a solution is made less concentrated (or more dilute) by the addition of solvent. For example, a glass of iced coffee becomes increasingly dilute, and less sweet, as the ice melts. In laboratories, solutions are often stored in their concentrated forms, called stock solutions. Solutions of lower concentrations are prepared from stock through dilution.

<img alt="Dilution formula \(M_1V_1=M_2V_2\), equation, chemistry calculation, concentration adjustment." src="/files/core/CDNSource/lessons/1021/1021_Equations-02.png" style="height: 40px;" data-altupdatedat="1761830439000" data-alt="Eq2" />

where M and V are concentration and volume, respectively, and the subscripts &#8220;1&#8221; and &#8220;2&#8221; refer to the solution before and after the dilution, respectively. 
Now, since the product of molarity and volume equals moles, the number of moles before and after dilution stays the same.

<img alt="Mole equation M1V1=n1, formula for calculating solute amount in solution, chemistry study." src="/files/core/CDNSource/lessons/1021/1021_Equations-03.png" style="height: 40px;" data-altupdatedat="1761830439000" data-alt="Eq3" />

<img alt="Molarity calculation formula M&#8322;V&#8322;=n&#8322;, chemical equilibrium, equation diagram." src="/files/core/CDNSource/lessons/1021/1021_Equations-04.png" style="height: 40px;" data-altupdatedat="1761830439000" data-alt="Eq4" />

<img alt="Static equilibrium equation n&#8321;=n&#8322;; formula illustration for balance in physics or engineering studies." src="/files/core/CDNSource/lessons/1021/1021_Equations-05.png" style="height: 40px;" data-altupdatedat="1761830439000" data-alt="Eq5" />

Thus, dilution does not change the amount of solute in the solution.

This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/3-3-molarity">OpenStax Chemistry 2e, Section 3.3: Molarity.</a>

The relative amount of a given solution component is known as its concentration. Often, though not always, a solution contains one component with a ...

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Chemical Quantities and Aqueous Reactions

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KEY TERMS AND CONCEPTS

molarity and dilution in solutions

Molarity and dilution are key ideas for describing solution concentration. Concentration means the relative amount of one component in a solution. In many solutions, one component is present in much larger amount. That component is the solvent, which acts as the medium that holds the other parts dissolved or dispersed.

Water is a very common solvent, so aqueous solutions are common on Earth. A solute is the component present at a much lower concentration than the solvent. Chemists often describe solutions with simple terms such as dilute, which means relatively low concentration, and concentrated, which means relatively high concentration.

Concentration can also be measured with units. Molarity, written as M, is a useful unit in chemistry. It means the number of moles of solute in exactly 1 liter of solution, with units of mol/L. The molarity equation uses the total solution volume, not just the solvent volume, because the solute can change the final volume. Since solution volume can change with temperature, molarity can also change when temperature changes.

Dilution is the process of making a solution less concentrated by adding more solvent. A glass of iced coffee becomes more dilute, and less sweet, as the ice melts. In the lab, concentrated solutions are often kept as stock solutions. Scientists then prepare lower-concentration solutions from the stock by dilution.

During dilution, the number of moles of solute stays the same. That is why the equation M1V1 = M2V2 is used before and after dilution. Here, M stands for molarity and V stands for volume. The subscripts 1 and 2 show the solution before and after dilution. Because molarity times volume equals moles, dilution changes concentration and volume, but not the amount of solute.

Molarity and Dilution in Solutions

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Molarity and dilution are key ideas for describing solution concentration. Concentration means the relative amount of one component in a solution. In many solutions, one component is present in much larger amount. That component is the solvent, which acts as the medium that holds the other parts dissolved or dispersed. Water is a very common solvent, so aqueous solutions are common on Earth. A solute is the component present at a much lower concentration than the solvent. Chemists often...

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key terms and concepts

Learn how molarity measures solution concentration, why temperature can affect it, and how dilution from stock solutions changes concentration without changing solute amount.

Molarity and Dilution in Solutions | JoVE K12

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Molarity and Dilution in Solutions

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