Notes:Color Guide Gold : Important concept. Write this down. Orange : Definition. Write this down. Blue : Important information, but you do not need to copy. Red : Example. Copy if needed. White : General Discussion (Don’t Copy)

Chapter 7: Solutions Section 1: Solutions & Mixtures Sodium Chloride: Liquid Solution Air : Gaseous Solution

Mixtures of different substances exist all around us. Many of these mixtures are invisible, and we never notice them. Definition: mixture – a combination of different substances that is NOT formed by chemical reactions.  Mixtures can be separated!

All matter is either a pure substance or a mixture of other substances. Definition: pure substance – matter that always has the same chemical formula.  ALL elements are pure substances by themselves. Water is a pure substance. It is ALWAYS H 2 O. Kool-Aid is a mixture. It isn’t always the same. Mercury is a pure substance. It’s chemical formula is ALWAYS Hg.

Mixtures can be categorized into two groups: Heterogeneous and Homogeneous  Definition: heterogeneous mixture (HT) – a mixture that is not evenly dispersed.  Dispersed means “spread out”.  The particles in a HT mixture can be seen. Orange juice with pulp is an example of a heterogeneous mixture.

Heterogeneous Mixture Clear Orange Juice Orange Juice Pulp

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

There are a few different types of heterogeneous mixtures:  Definition: suspension – HT mixture in which particles are floating (suspended) in a fluid.  Many suspensions will “settle” over time.  Examples: Muddy Water Dusty Air Orange Juice with Pulp Salad Dressing

The particles of a suspension will eventually settle.

There are a few different types of heterogeneous mixtures: –Definition: colloid – a suspension made of particles too small to settle out. –Examples: Mayonnaise Milk Whipped Cream Butter

Homogeneous mixtures look the same all over. Definition: homogeneous mixture (HM) – a mixture in which the particles are spread evenly.  The particles that make up a HM mixture cannot be seen.  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.

+ = +

The tea looks the same throughout the pitcher.

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

Two or more solids can form solutions also.  Definition: alloy – a metal solution made from two or more solids.  Examples:  Steel – iron and carbon  Brass – copper and zinc  Bronze – copper and tin

In order to make an alloy, the metals must be melted.  While melted, the metals are mixed with solutes to form a solution. + Tin Copper Bronze

Chapter 7: Solutions Section 2: How Substances Dissolve

Solutions are formed by the process of dissolving.  Definition: dissolving – the process by which substances mix to form a solution. These tablets are dissolving in the water to form a solution.

When substances dissolve, they are pulled apart into ions or molecules.  Of course, these are too small to see. Definition: solute - a substance that gets dissolved. Definition: solvent - a substance that does the dissolving.

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

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

Making a solute smaller makes it dissolve faster.  By crushing up a solute, you increase the surface area.  The solvent can pull the solute apart faster when it is smaller. Rock Salt Crushed Salt

Stirring or shaking will make a SOLID solute dissolve faster.

Heating the solvent will make a SOLID solute dissolve faster. Faster moving atoms means faster dissolving! Which one will dissolve sugar Fastest?

Did you know that liquids can dissolve gases? Fish and other aquatic life breathe oxygen that has dissolved into water. Liquids dissolve gases best when:  The liquid is cold.  The liquid is under lots of pressure. CO 2 Gas is also dissolved into your soda!

Water is very good at dissolving things.  Water is known as “The Universal Solvent”  Water can dissolve any ionic compound, and many covalent compounds.

The water molecule has a positive end and a negative end.  This is called being “polar”. H H O Because water is polar, it can attract molecules and ions like a magnet. Na Cl

Because water’s + and – charges are not spread out evenly, it is “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. The Earth is Polar! It has two separate sides.

Water can only dissolve other polar compounds.  If water cannot dissolve a substance, then that substance is “nonpolar”. Water and Vinegar? No Problem! Water and Oil? NO WAY.

Oil is Nonpolar Water is Polar They cannot mix. Water can only dissolve other polar substances!

 Definition: nonpolar compound – has an even charge on its molecules.  The charges are spread out evenly.  Nonpolar substances can only dissolve other nonpolar substances.  Example – oil-based paint will not dissolve in water. A nonpolar solvent must be used.

Chapter 7: Solutions Section 3: Solubility & Concentration

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.

The amount of solute dissolved in a solvent affects its concentration.  Definition: concentration – a description of the amount of a solute in a certain amount of solution.  Think of concentration as being how “strong” a solution is. Not Very Concentrated Very Concentrated

“Concentrated” substances have lots of solute. “Diluted” substances only have a little solute. Add water to OJ concentrate to dilute it.

The “3%” tells you that the H 2 O 2 is not very concentrated, and is safe to touch.

The “35%” tells you that the H 2 O 2 is more concentrated, and NOT safe to handle!

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 solute.  Definition: unsaturated – a solution that CAN hold more solute.

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.  A HOT solution can hold lots of solute.  When it COOLS, it becomes supersaturated.

Supersaturated solutions are unstable.  The extra solute can “fall out” if the solution is shaken! The crystals in the supersaturated solution were “shaken out”!

Some solutions have the ability to conduct electricity… Definition: electrolyte – a solution that can conduct electricity.  Most electrolytes contain ionic compounds.

 All ionic compounds form electrolytes.  Covalent compounds cannot conduct electricity when dissolved in a solution.  They are called nonelectrolytes. Definition: nonelectrolyte – a solution that does not conduct electricity.