Types of Solutions

Important WATER Fact: δ- δ+ Water is able to dissolve most ionic and polar covalent compounds because its molecules are so polar. δ- δ+ When water is the solvent of a solution, we refer to it as aqueous solution.

Important WATER Fact: The ratio of hydrogen to oxygen (H:O) is always 2:1. Water always has 2 hydrogen and 1 oxygen. This will not change without performing a chemical reaction.

Dissolution What happens to a substance when it dissolves. When substances dissolve, they simply break apart into their smallest particles. These are too tiny to see, so it often looks like they disappear. When ionic compounds dissolve, they break apart into their ions.

Solubility Saturated Solutions A solution is saturated when a solvent has dissolved all the solute it can at a certain temperature. At room temperature (20oC), 36 grams of NaCl will dissolve in 100 mL of water. Image courtesy of Sergei Smirnov, NMSU

Solubility Unsaturated Solutions A solution is unsaturated when more solute can still be dissolved at a given temperature. At room temperature (20oC), 36 grams of NaCl will dissolve in 100 mL of water. Image courtesy of Sergei Smirnov, NMSU

Supersaturated Solutions Solubility Supersaturated Solutions A solution is supersaturated when more solute is dissolved than normally allowed at a given temperature. When a solution is heated, more solid solute can be added. As it cools, the excess solute crystallizes and falls to the bottom of the beaker. (This is known as precipitation.) Supersaturation occurs because some compounds, like sodium acetate, cannot reform crystals without a rough surface or a seed crystal.

To supersaturate a solution, you heat up a solution to allow a large amount of solute to dissolve. Extra Dissolved Solute Then you allow the solution to cool. In most solutions, the extra solute will spontaneously precipitate, but some solutes will remain dissolved. These supersaturated solutions are unstable, and as soon as the solution is agitated too much or a seed crystal is added, the extra solute will crystallize.

If 100 grams of KNO3 were dissolved in 100 grams of water at 65oC, would the solution be saturated, unsaturated, or supersaturated? Unsaturated

If 169 grams of KNO3 were dissolved in 100 grams of water at 80oC, would the solution be saturated, unsaturated, or supersaturated? Saturated

If 80 grams of KBr were dissolved in 100 grams of water at 80oC, would the solution be saturated, unsaturated, or supersaturated? Unsaturated

If 115 grams of KBr were dissolved in 100 grams of water at 95oC, would the solution be saturated, unsaturated, or supersaturated? Supersaturated

Decide whether the solutions on your notes are saturated, unsaturated or supersaturated.

Electricity Electricity is made up of tiny subatomic particles known as electrons. These are the same electrons found around every atom. When we measure how well electricity can pass through a substance, we are measuring its conductivity.

We can determine the relative conductivity of a substance using a conductivity tester. If the lightbulb lights up, then the solution is conducting electricity well. If the lightbulb does NOT light up, then the solution is conducting electricity poorly or not at all.

Does water conduct electricity very well? NO! Pure water does not conduct electricity well.

When ionic compounds dissolve in water, the concentration of ions increases. These ions are able to conduct electricity. Ionic compounds that conduct electricity when they are dissolved are known as Electrolytes

So why is water so dangerous around electricity? Water is very rarely pure. Tap water and water from oceans and lakes contain dissolved minerals. These minerals are ionic compounds which conduct electricity. They are electrolytes! Photo by M Disdero

Solubility In order to be an electrolyte, a compound must be ionic AND soluble. If it is not soluble, it will not break apart into the ions that conduct electricity. PbI2 Lead (II) iodide would not be an electrolyte because although it is ionic, it is not soluble.

It is important that you understand that ionic substances must be dissolved in order to conduct electricity. If they are not dissolved, then they will not conduct electricity. Solid NaHCO3 Dissolved NaHCO3

Electrolytes Steps to determining if a substance will be an electrolyte: Step 1: Determine if the substance is ionic or covalent. If it is covalent, it is NOT an electrolyte. If it is ionic, continue to step 2. Step 2: Determine if the ionic compound is soluble. If the compound is insoluble, it is NOT an electrolyte. If the compound is soluble and ionic, then it is an electrolyte.

CuSO4 Electrolytes Is copper (II) sulfate an electrolyte? 1. Determine if the substance is ionic or covalent. CuSO4 is ionic 2. Determine if the ionic compound is soluble. CuSO4 is ionic and soluble, so it is an electrolyte. CuSO4 is soluble.

C12H22O11 Electrolytes Is sucrose an electrolyte? 1. Determine if the substance is ionic or covalent. C12H22O11 is covalent C12H22O11 is covalent, so it is NOT an electrolyte.

CaCO3 Electrolytes Is calcium carbonate an electrolyte? 1. Determine if the substance is ionic or covalent. CaCO3 is ionic 2. Determine if the ionic compound is soluble. CaCO3 is ionic but insoluble, so it is NOT an electrolyte. CaCO3 is insoluble.

We learned earlier that water is not a good conductor or electricity We learned earlier that water is not a good conductor or electricity. Based on what we just learned, why doesn’t water conduct electricity very well? Water does not conduct electricity very well because it is a covalent compound. Pure Water

Determine if the compounds on your notes are electrolytes (E) or nonelectrolytes (X).