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Important Vocabulary
Solution: another name for a homogeneous mixture.
Aqueous Solution: a solution where water is the solvent.
Solvent: the substance that exists in the greatest quantity in a solution.
Solute: any substance in a solution other than the solvent
Concentration: the amount of a particular solute in a given amount of solution.
Dilution: a reduction in the concentration of a particular solute by adding more solvent to a solution.
Solubility: the maximum amount of solute that can dissolve in a given amount of solvent at a given temperature and pressure.
Lesson 1.3 Properties of Solutions
Lesson 1.3 Properties of Solutions
Aqueous Solutions
‘You might recall that a homogeneous mixture is a mixture in which two or more pure substances are evenly mixed. Another name for a homogeneous mixture is a solution. In a solution, substances are evenly mixed in a way that you cannot easily identify where each part is. For example, when you look at the air around you, it is made up of oxygen, nitrogen, and many other gases, but you are not able to easily identify each different gas.
For every solution, the process of dissolving will take place. This could be sugar into tea to sweeten it up or salt into hot water to help a sore throat. A solution in which water is the solvent is called an aqueou solution.
Solutes and Solvents
Scientists use two terms to refer to the substances that make up a solution— solute and solvent. Generally, the solvent is the substance that exists in the greatest quantity in a solution. This means that a solute is any substance in a solution other than the solvent. For example, air is a solution of 78 percent nitrogen, 21 percent oxygen, and 1 percent other substances. Which substance is the solvent? In air, nitrogen exists in the greatest quantity. Therefore, it is the solvent. The oxygen and other substances are solutes. In any solution there will always be a solute and a solvent. Even if the quantities are very similar, one substance in the solution will exist in a greater quantity than any other substance.
Types of Solutions
When you think of a solution, you might think of a liquid. However, solutions can exist in all three states of matter—solid, liquid, or gas. The state of the solvent, because it exists in the greatest quantity, determines the state of the solution.
In the Types of Solutions table, you can see a variety of combinations to create different solutions. When combined, a solid solvent and a gas or solid solute will create a solid state for the solution. A liquid solvent and a solid, liquid, or gas solute will create a liquid state for the solution. Lastly, a gas solvent with a gas solute results in a solution in a gaseous state.
Making Changes to Aqueous Solutions
Since water is the solvent for all aqueous solutions, solutes determine what we might call the strength or weakness of an aqueous solution. For example, this happens when you don't put enough drink mix powder in a pitcher of water or when you put in too much. In order for you to make changes to your drink to get it to taste just right, you either have to add more solute (drink mix) or you have to add more solvent (water).
Concentration
Have you ever tasted a spoonful of soup and wished it had more salt in it? In a way, your taste buds were measuring the amount, or concentration, of salt in the soup. Concentration is the amount of a particular solute in a given amount of solution. In the soup, salt is a solute. Saltier soup has a higher concentration of salt. Less salty soup has a lower concentration of salt. When we think of concentration in our everyday life, we think of putting a certain amount of focus on a given task. This is similar to how the scientific use of the word concentration is a certain amount of solute put in the solution; you are the solution, and the amount of focus is your solute.
Dilution
One way to describe the saltier soup is to say that it is more concentrated. The less salty soup is more dilute. Dilution is a reduction in the concentration of a particular solute by adding more solvent to a solution. This can be done by increasing the amount of soup in this example. By doing this, the ratio of soup (solvent) to salt (solute) has changed, and the amount of solvent has increased. This is not saying that the solute and solvent have changed, only that there was an increase in the amount of solvent itself.
Another example of this is coffee and creamer. In this case, coffee is the solvent, which makes creamer the solute. If you don't enjoy the strong coffee flavor, you add creamer. Sometimes it is hard to get that perfect ratio, and you add too much and lose that coffee taste. To fix this, you add more coffee, diluting the
creamer-to-coffee ratio.
In Table 2 the ratio of sugar to solution determined how diluted the solution was. When describing a solution, dilution and concentration can both be used to describe the same solution. For example, you can say a solution has a low concentration of sugar, or you can say the solution is diluted and has a low amount of solute to solvent. In both descriptions, the solution being described is the same.
The terms concentrated and dilute can be used to describe how much solute is dissolved in a solution. However, these terms don't state the exact amount or quantity of solute dissolved. What one person thinks is concentrated might be what another person thinks is diluted. For example, soup that tastes too salty to you might be perfect for someone else. How can concentration be described more precisely?
Quantity of Solute
A more precise way to describe concentration is to state the quantity of solute in a given quantity of solution. When a solution is made of a solid dissolved in a liquid, such as salt in water, concentration is the mass of solute in a given volume of solution. Mass usually is stated in grams, and volume usually is stated in liters, like a liter of soda. For example, concentration can be stated as grams of solute per 1 L of solution. However, concentration can be stated using any units of mass or volume.
Dissolving of Solutes
Have you ever put too much sugar into a glass of iced tea? What happens? Not all of the
sugar dissolves. You stir and stir, but there is still sugar at the bottom of the glass. That is
because there is a limit to how much solute (sugar) can be dissolved in a solvent (water).
Solubility is the maximum amount of solute that can dissolve in a given amount of
solvent at a given temperature and pressure. If a substance has a high solubility, more of
it can dissolve in a given solvent
Saturation
If you add water to a dry sponge, the sponge absorbs the water. If you keep adding water, the sponge becomes saturated. It can’t hold any more water. This is similar to what happens when you stir too much sugar into iced tea. Some sugar dissolves, but the excess sugar does not dissolve. The solution s saturated. A saturated solution is a solution that contains the maximum amount of solute the solution can hold at a given temperature and pressure. An unsaturated solution is a solution that can still dissolve more solute at a given temperature and pressure.
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