Chapter 7: Solutions Section 1: Solutions VS Mixtures Sodium Chloride Liquid Solution Air is a Gaseous Solution

Mixtures of different substances exist all around us. –Many of these mixtures are invisible, and we never notice them. –However, some mixtures can easily be identified. What is a mixture?

All matter is either a pure substance or a mixture of other substances. –Definition: pure substance – matter that has a fixed chemical composition. For example: What is a mixture? Water is a pure substance. It is ALWAYS H 2 O. Kool-Aid is a mixture of water and other substances.

Mixtures can be categorized into two groups: –Heterogeneous and Homogeneous –Definition: heterogeneous mixture – a mixture made of visibly different substances. The particles in a het. Mixture are not spread evenly. Orange juice with pulp is an example of a heterogeneous mixture. Types of Mixtures

Heterogeneous Mixture Clear Orange Juice Orange Juice Pulp

Heterogeneous Mixtures Different fragments make up this rock. This rock is a heterogeneous mixture.

Homogeneous mixtures look the same all over. –Definition: homogeneous mixture – a mixture in which the particles are spread evenly. –Sweet tea is an example of a homogenous mixture. –There are several different substances (tea, water, and sugar) but you cannot see them. The tea looks uniform (the same) throughout. Homogeneous Mixtures

+ = +

The tea looks the same throughout the pitcher.

We can call homogeneous mixtures by another name: solutions. –Definition: solution - a homogenous mixture of 2 or more substances that are evenly dispersed. Solutions

Many solutions are formed by dissolving one substance into another substance. –These tablets are dissolving in the water to form a solution. Solutions

It is important to know what makes up a solution. All solutions are made of solutes and solvents. –Definition: solute - a substance that dissolves into another substance. –Definition: solvent - a substance that a solute is dissolved into. What is in a Solution?

For example: –When you stir sugar into water, the sugar dissolves. –The water is the solvent. –The sugar is the solute. Solvents Solute SolventSolution + =

Water is very good at dissolving things. –Water is known as “The Universal Solvent” The Universal Solvent

Not all solutions contain water! Other states of matter can be solutions. –Gases & Solids can form solutions also. –Air is an example of a gaseous solution. –Air is composed of lots of different gases that we cannot see. Other types of Solutions

2 or more solids can form solutions also. –Metal alloys are homogenous mixtures that contain a metal mixed with another substance. –Some examples are: Steel – iron and carbon Brass – copper and zinc Bronze – copper and tin Metal Alloys

In order to make an alloy, the metals must be melted. –While melted, the metals are mixed to form a solution. Metal Alloys + TinCopper Bronze

Chapter 7: Solutions Section 2: How Substances Dissolve

Water can dissolve ionic compounds because of its structure. –The electrons in the hydrogen atoms are pulled toward the oxygen atom. –This gives the oxygen atom a slight negative charge. –The hydrogen atoms gain a slight positive charge. How do things dissolve?

The Water Molecule Oxygen HH

Because water’s + and – charges are not spread out evenly, it becomes “polar”. –Definition: polar compound – a molecule that has a positive side and a negative side. Because water is a polar compound, it is a good solvent. Polar Compound

–In chemistry, a rule of thumb is that “like dissolves like.” –Water is a polar compound, so it can dissolve other polar compounds. –If water cannot dissolve a substance, then that substance is “nonpolar”. Like dissolves Like

–Definition: nonpolar compound – a compound that has no charge on its molecules.. Nonpolar compounds can only dissolve other nonpolar substances. Example – oil-based paint will not dissolve in water. A nonpolar solvent must be used. Nonpolar Compound

Polar vs. Nonpolar Oil is Nonpolar They cannot mix. Water is Polar

We have all seen solutes dissolve into solvents before. And we all *probably* know some ways to speed up the process. The Dissolving Process

Making a solute smaller makes it dissolve faster. –By crushing up a solute, you increase the surface area. The Dissolving Process Rock Salt Crushed Salt

Stirring or shaking will make a solute dissolve faster. The Dissolving Process

Increasing the solvent’s temperature will make the solute dissolve faster. The Dissolving Process Which one will Dissolve sugar Fastest?

Did you know that liquids can dissolve gases? Fish and other aquatic life breath oxygen that has dissolved into water. Liquids dissolve gases best when they are cold. The Dissolving Process: Gases

Don’t believe it? Well, consider this… –Which makes a louder “whoosh” sound when opened… a hot soda or a cold one? The Dissolving Process: Gases

Some substances dissolve easier than others. This property is called “solubility” Definition: solubility – the max amount of a solute that will dissolve in a certain amount of solvent. Substances have different solubility. –Some will dissolve completely in water, while others will dissolve only a small amount. Solubility

The amount of solute dissolved in a solvent affects its concentration. –Think of concentration as being how “strong” a solution is. –Definition: concentration – the amount of a substance in a certain amount of solution. Concentration

“Concentrated” substances have lots of solute. “Diluted” substances only have a little solute. Concentration

When a solvent can no longer hold any more solute, we called it “saturated”. –Definition: saturated solution – a solution that cannot dissolve any more of a given solute. –Definition: unsaturated – a solution that CAN hold more solute. Saturated / Unsaturated

Sometimes, a solvent can be made to hold more solute than normal. –The solution is called “supersaturated”. –Definition: supersaturated – a solution that has more solute than normal. Super Saturated

Supersaturated solutions are unstable. –The extra solute can “fall out” at any time. Super Saturated