Chemical Solutions

Solvents and Solutes

Hi, and welcome to this video about solutions! To review before we get started: There are two parts of a solution: the solvent, which does the dissolving, and the solute, which gets dissolved. In general, the solvent is the largest component of the solution and the solute is the smallest component. Let’s head to the kitchen to talk about solutions further!

First, let’s boil some water for pasta. The water needs to be seasoned, so we’ll add salt to be dissolved in the water, making a saltwater solution. The salt is the solute, and the water is the solvent.

Some things do not dissolve in certain solvents. Take vinegar and olive oil for example. The two components stay separated even when they are in the same vinaigrette salad dressing. We can shake the bottle as much as we want, but the two liquids never dissolve. This is an example of like dissolves like, which means solvents dissolve solutes that have a similar chemical nature. Water likes to dissolve things that have a slight charge to them because water is polar. Oil does not have a charge, and it is not polar. Since the two chemical charges are different, they do not dissolve. Water will easily dissolve sugar and salt because these solutes are polar, but they will not dissolve in oil because oil is not polar.

Another thing that we know very well that also dissolves in water: Soap. Soap is made from a mixture of different salts that come from fatty acids. When it comes to solutions, soap is a bit of a special case. It has a molecule that has two pieces: a polar head that easily dissolves in water and a nonpolar tail that likes dissolving in oil. That’s why soap is used to clean dishes, your hands, and other dirty things. The soap helps water dissolve nonpolar things, like oil and dirt. So when we are finished eating our salad with vinaigrette, we can wash the olive oil away using soap and water!

Solution Variables

Now, let’s talk about concentrated solutions and diluted solutions. Let’s make some lemonade to demonstrate. We’ll start with this frozen lemonade concentration. The reason it’s called a concentration is that this is a concentrated solution of lemon juice, water, and sugar, meaning there is a lot of lemon juice and sugar dissolved in just a little bit of water. If we drank just the concentrate, it would be overpowering! Too much lemon and sugar in one sip! So, we add the lemonade concentrate to water. However, if we add too much water, we won’t be able to taste the lemon at all. We’ll have made a dilute solution, meaning there is hardly any solute dissolved in the solvent.

How well a liquid dissolves solids is typically temperature-dependent. We can dissolve a certain amount of sugar in room temperature water. However, rock candy is created using a supersaturated solution of sugar in water. First, water is brought to a boil; this increases the solvent’s temperature. Then, sugar is added, A LOT of sugar– more sugar than we can dissolve at room temperature. After it dissolves, the sugar water is brought down to room temperature. Now, we can make rock candy by dipping a string in the water and letting the water evaporate. We have to be very careful though! If we add any more sugar to the solution once it is room temperature, all of the extra sugar will simply fall to the bottom of the solution, unable to be dissolved. A supersaturated solution means the solvent dissolved more solute than it should have been able to!

Temperature also changes how fast something dissolves. When I was making pasta, I poured salt in the pot when the water was at room temperature. The salt sat at the bottom, very slowly dissolving. However, as the pot heated, the salt dissolved faster and faster!

Let’s recap! A solution is made of a solvent which dissolves a solute. Like dissolves like means solvents easily dissolve solutes that have similar properties. A dilute solution has little solute while a concentrated solution has a lot. How easily something dissolves and how much depends on the temperature of the solvent.

Here’s a review question!

Review Question

Why do we boil water to make tea?

1. Because that’s how we’ve always done it.
2. Because we need to create a supersaturated solution.
3. Because the flavors from the tea more easily dissolve in hot water.

Thanks for watching, and happy studying!