Molarity and Dilutions Photo by Chris73

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 as long as the substance remains water.

What does it mean that oxygen is more electronegative than hydrogen? Oxygen pulls harder on the electrons in the bonds of water than hydrogen does. This is what makes water POLAR!

Because water molecules are polar, water is able to dissolve most ionic and polar covalent compounds. δ- δ+ When water is the solvent of a solution, we refer to it as aqueous solution.

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.

Like we said, water can dissolve many compounds because of its polar nature. The amount of solute that has been dissolved in a certain amount of solution is known as the concentration of the solution.

[NaCl] = 1.5 M This is a 1.5 molar solution In chemistry, the most common measure of concentration is molarity (M). moles of solute liter of solution Molarity = If 3.0 moles of NaCl are dissolved in 2.0 liters of solution, what is the molarity of the solution? 3.0 mol NaCl / 2.0 L solution = 1.5 M [NaCl] = 1.5 M This is a 1.5 molar solution

Calculating Molarity Step 1: Determine the number of moles of solute. If you are given grams, then divide by formula mass to get moles. Step 2: Determine how many liters of solution. If you are given milliliters, then divide by 1000 mL/L to get liters. Step 3: Divide moles of solute by liters of solution. Be careful, if you are given moles or liters, don’t try to convert them. Just use them!

You can increase the concentration of a solution by adding more solute until in has become saturated. You can dilute a solution by adding more solvent. For aqueous solutions, dilution is often termed “watering down” the solution.

Calculating Dilutions In chemistry, there is a simple equation for calculating the amount of solvent that would need to be added to a solution. Step 1: Determine which set of volume and molarity measurements belong together. (Place these on the same side of the equation.) Step 2: Determine which measurement is by itself. (Place this on the other side of the equation with your unknown.) Step 3: Divide the original set of numbers by the individual measurement. Important Fact: The unit of volume you start with is the one you will end with!