What is the term for a solution containing more that the maximum solute that can dissolve at a given temperature?

Have you ever made chocolate milk with too much syrup? Some of the extra remains undissolved at the bottom of the glass. That’s because the milk has become a saturated solution, a solution containing the maximum concentration of one or more dissolved solutes in a solvent. In this case, the syrup would be the solute, and the milk the solvent. In a saturated solution, additional solutes won't dissolve (just like the extra chocolate syrup).

Unsaturated solutions contain a smaller amount of solute than what can dissolve, leaving no remainder.

• If you were to add more solute to an unsaturated solution, it would dissolve into the solvent because the solution has not yet reached saturation.
• Adding just a teaspoon of chocolate syrup to a glass of milk would produce an unsaturated solution because the solute concentration is below the capacity of the solvent to dissolve.

Supersaturated solutions contain more than the maximum amount of dissolved solute than the solution is able to dissolve at a given temperature.

• Supersaturated solutions remain solvated even when they are cooled with additional solids.
• Sodium acetate in water, is an example of a supersaturated solution.
• Solvents that can be heated safely, like water, are often used in supersaturated solutions.

TYPES OF SATURATION

1. SATURATED SOLUTION

• In a saturated solution, there is so much solute present that if more were added, it would not dissolve.
• A solution is saturated when the rates of solubility and crystallization are equal and dynamic equilibrium is reached.

See the image below to visualize what a saturated solution looks like.

Source

• The above image shows the beginning of the immersion interaction, where the strong solute begins dissolving (as represented by the red arrows).
• A significant portion of strong solute (as evidenced by the blue arrows in the following measurement glass in the second figure) has broken down, but not entirely, since the crystallization process has not yet been completed.
• Some components of dissolvable solute are undissolved in the last container.
• During this interaction, the outlay of crystallization is equal to the rate of disintegration (see the equal size of the red and blue arrows), resulting in a fully saturated solution.

2. UNSATURATED SOLUTION

• A solution with less solute than the solution is capable of dissolving is called an unsaturated solution.
• Solutes in an unsaturated solution dissolve completely, leaving no remaining substrates.

See the image below to visualize an unsaturated solution.

Source

• The first figure shows the beginning of the interaction in which a strong solute is starting to dissolve.
• The second figure shows that the solute has dissolved significantly and that the disintegration rate is greater than the crystallization rate, as is depicted by the size difference between the red and blue arrows.
• Total dissolution of the solute is reached in the third container.

3. SUPERSATURATED

• A supersaturated solutions contain more than the maximum amount of dissolved solute than the solution is able to dissolve at a given temperature.
• A supersaturated solution can remain in a state of complete dissolution when cooled, and the crystallization of the excess solute can be instigated by the addition of a solute crystal called a seed crystal.
• Let’s take a look at a supersaturated solution in the image below.

Source

• The first image shows a container with a large amount of solute that has started to dissolve (red arrows).
• In the second image, the rate of dissolution has become less than the pace of disintegration (blue arrows).
• In the last image, the rate of dissolution is far lesser than the rate of crystallization, resulting in a solid precipitate that does not dissolve.

Mass Percent

Mass percent expresses the concentration of a solution when both the mass of the solute and solution are given. To find mass percent, use the following formula:

Mass % = msolute/msolution x 100%

Where msolute = mass of solute

msolution = mass solution

Let’s try out a practice problem with a supersaturated solution example:

1. What is the mass percent of sodium hydroxide in a solution that is made by dissolving 8.00g NaOH in 50.00g H2O?

Knowns: msolute = 8.00g NaOH

and msolution = 50.0g H2O

Solving for mass percent

Mass % = msolute/msolution x 100%

Mass % = (8.00g)/(8.00g + 50.00g) x 100%

Mass % = (8.00g)/(58.00g) x 100%

Mass % = = 13.8% NaOH solution.

FACTORS AFFECTING SATURATION

• With the exception of compounds containing anions, the solubilities of ionic solutions increase as the temperature rises.
• A finely divided solid is more soluble because it has a higher surface area to volume ratio.
• Contrary to the rate of solubility, which is largely influenced by temperature, the rate of crystallization is largely influenced by the concentration of the solute on the surface of the seed crystal.
• The concentration of the solute at the surface of a still solution increases crystallization. Stirring the solution prevents the build-up and maximizes the net dissolution rate.
• A net dissolving rate is calculated by subtracting the dissolving rate from the crystallization rate.

• There are three types of solution saturation: saturated, unsaturated, and supersaturated.
• A saturated solution is a solution containing the maximum concentration of one or more dissolved solutes in a solvent
• An unsaturated solution contains less solute than the solution is capable of dissolving.
• Supersaturated solutions contain more dissolved solute than saturated solutions and dissolves more solute than the solution has the capacity to at a given temperature.

FAQs

1. What is meant by supersaturated solutions?

A solution that contains more solute than the solvent is capable of dissolving. It has more undissolved solute than the saturated solution that tends to crystallize and precipitate with the help of a seed crystal.

2. How do you know if a solution is supersaturated?

If the solution is supersaturated, crystals will very quickly form around the solute you've added.

3. What are the examples of supersaturated solutions?

The supersaturated solution contains more dissolved substances than a saturated solution. For example, 40g NaCl in 100ml H2O. The additional 4.0g NaCl remains undissolved.

4. What are the saturated and supersaturated solutions?

The solution obtained by dissolving the maximum amount of solute at a given temperature is known as a saturated solution. A solution that contains more amount of solute than the required to saturate is known as a supersaturated solution.

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REFERENCE

Learning Objectives

1. Learn some terminology involving solutions.
2. Recognize which terminology is qualitative and which terminology is quantitative.
3. Explain why certain substances dissolve in other substances.

The major component of a solution is called the solventThe major component of a solution.. The minor component of a solution is called the soluteThe minor component of a solution.. By major and minor we mean whichever component has the greater presence by mass or by moles. Sometimes this becomes confusing, especially with substances with very different molar masses. However, here we will confine the discussion to solutions for which the major component and the minor component are obvious.

Solutions exist for every possible phase of the solute and the solvent. Salt water, for example, is a solution of solid NaCl in liquid water; soda water is a solution of gaseous CO2 in liquid water, while air is a solution of a gaseous solute (O2) in a gaseous solvent (N2). In all cases, however, the overall phase of the solution is the same phase as the solvent.

A solution is made by dissolving 1.00 g of sucrose (C12H22O11) in 100.0 g of liquid water. Identify the solvent and solute in the resulting solution.

Solution

Either by mass or by moles, the obvious minor component is sucrose, so it is the solute. Water—the majority component—is the solvent. The fact that the resulting solution is the same phase as water also suggests that water is the solvent.

Test Yourself

A solution is made by dissolving 3.33 g of HCl(g) in 40.0 g of liquid methyl alcohol (CH3OH). Identify the solvent and solute in the resulting solution.

Answer

solute: HCl(g); solvent: CH3OH

One important concept of solutions is in defining how much solute is dissolved in a given amount of solvent. This concept is called concentrationHow much solute is dissolved in a given amount of solvent.. Various words are used to describe the relative amounts of solute. DiluteA solution with very little solute. describes a solution that has very little solute, while concentratedA solution with a lot of solute. describes a solution that has a lot of solute. One problem is that these terms are qualitative; they describe more or less but not exactly how much.

In most cases, only a certain maximum amount of solute can be dissolved in a given amount of solvent. This maximum amount is called the solubilityThe maximum amount of a solute that can be dissolved in a given amount of a solvent. of the solute. It is usually expressed in terms of the amount of solute that can dissolve in 100 g of the solvent at a given temperature. Table 11.2 "Solubilities of Some Ionic Compounds" lists the solubilities of some simple ionic compounds. These solubilities vary widely: NaCl can dissolve up to 31.6 g per 100 g of H2O, while AgCl can dissolve only 0.00019 g per 100 g of H2O.

Table 11.2 Solubilities of Some Ionic Compounds

When the maximum amount of solute has been dissolved in a given amount of solvent, we say that the solution is saturatedA solution with the maximum amount of solute dissolved in it. with solute. When less than the maximum amount of solute is dissolved in a given amount of solute, the solution is unsaturatedA solution with less than the maximum amount of solute dissolved in it.. These terms are also qualitative terms because each solute has its own solubility. A solution of 0.00019 g of AgCl per 100 g of H2O may be saturated, but with so little solute dissolved, it is also rather dilute. A solution of 36.1 g of NaCl in 100 g of H2O is also saturated but rather concentrated. Ideally, we need more precise ways of specifying the amount of solute in a solution. We will introduce such ways in Section 11.2 "Quantitative Units of Concentration".

In some circumstances, it is possible to dissolve more than the maximum amount of a solute in a solution. Usually, this happens by heating the solvent, dissolving more solute than would normally dissolve at regular temperatures, and letting the solution cool down slowly and carefully. Such solutions are called supersaturatedA unstable solution with more than the normal maximum amount of solute in it. solutions and are not stable; given an opportunity (such as dropping a crystal of solute in the solution), the excess solute will precipitate from the solution.

It should be obvious that some solutes dissolve in certain solvents but not others. NaCl, for example, dissolves in water but not in vegetable oil. Beeswax dissolves in liquid hexane but not water. What is it that makes a solute soluble in some solvents but not others?

The answer is intermolecular interactions. The intermolecular interactions include London dispersion forces, dipole-dipole interactions, and hydrogen bonding (as described in Chapter 10 "Solids and Liquids"). From experimental studies, it has been determined that if molecules of a solute experience the same intermolecular forces that the solvent does, the solute will likely dissolve in that solvent. So, NaCl—a very polar substance because it is composed of ions—dissolves in water, which is very polar, but not in oil, which is generally nonpolar. Nonpolar wax dissolves in nonpolar hexane but not in polar water. This concept leads to the general rule that “like dissolves like” for predicting whether a solute is soluble in a given solvent. However, this is a general rule, not an absolute statement, so it must be applied with care.

Would I2 be more soluble in CCl4 or H2O? Explain your answer.

Solution

I2 is nonpolar. Of the two solvents, CCl4 is nonpolar and H2O is polar, so I2 would be expected to be more soluble in CCl4.

Test Yourself

Would C3H7OH be more soluble in CCl4 or H2O? Explain your answer.

Answer

H2O because both experience hydrogen bonding

Key Takeaways

• Solutions are composed of a solvent (major component) and a solute (minor component).
• Concentration is the expression of the amount of solute in a given amount of solvent and can be described by several qualitative terms.
• Solubility is a specific amount of solute that can dissolve in a given amount of solvent.
• “Like dissolves like” is a useful rule for deciding if a solute will be soluble in a solvent.

Exercises

1. Define solute and solvent.

2. Define saturated, unsaturated, and supersaturated.

3. A solution is prepared by combining 2.09 g of CO2 and 35.5 g of H2O. Identify the solute and solvent.

4. A solution is prepared by combining 10.3 g of Hg(ℓ) and 45.0 g of Ag(s). Identify the solute and solvent.

7. Would the solution in Exercise 5 be described as dilute or concentrated? Explain your answer.

8. Would the solution in Exercise 6 be described as dilute or concentrated? Explain your answer.

11. Which solvent is Br2 more likely soluble in—CH3OH or C6H6?

12. Which solvent is NaOH more likely soluble in—CH3OH or C6H6?

13. Compounds with the formula CnH2n + 1OH are soluble in H2O when n is small but not when n is large. Suggest an explanation for this phenomenon.

14. Glucose has the following structure:

    What parts of the molecule indicate that this substance is soluble in water?

Answers

1. The solvent is the majority component of a solution, whereas the solute is the minority component of a solution.

3. solute: CO2; solvent: H2O

7. concentrated because there is a lot of solute

13. The nonpolar end dominates intermolecular forces when n is large.