Chemistry - Ch.6 Key Concepts

The Mole

A unit to express large numbers that is used to simplify the number of atoms/objects one is working with

• 1 mol = 6.022×10²³

Using Avogadro’s Number

One mole of atoms is any element equals the atomic mass in grams/mol

• EX: First, align units for cancelation, multiply across, and label units + convert to scientific notation

Calculation of Molar Mass

1. Count atoms

2. Add up atomic masses of all the atoms

Concentration

The ratio of solute in a solution to solvent (total solution)

Solute

A component of a solution that presents at a MUCH LOWER concentration than a solvent

Solvent

A component with a concentration that is SIGNIFICANTLY GREATER than that of all other components

Mass Percent

An element’s percentage of the total mass of the compound

• Mass % = mass of x in sample / mass of the sample (100%)

Converting mass % to grams

Assume you have an 100g sample of the compound

• 1.) convert percentage to a decimal

• 2.) Identidy the total mass

• 3.) Multiply :3

Determining the Empirical Formula

1. Assume 100g sample of compound to change % to grams

2. Convert the grams of each element into moles

3. Divide the mass of each element by its atomic mass (amu)

4. Divide the mole values of all the element by the smallest mole value of the compound

5. multiply all numbers by the smallest integer that converts subscripts into whole numbers

6. —> if whole numbers, use as subscript

Determining Molecular Formula from Empirical Formula and Molar Mass

1. Use: x formula units/ molecule = molecular/molar mass (AMU of g/mol)

2. Plug in: (AxBy)n = AnxBny

Molarity

A different way of representing concentration

• M = Mol Solute / L Solution

Volume Percentage

Volume Solute / volume solution

Mass-volume percentage

Mass Solute / volume solution

parts per million (ppm)

mass solutex10^6 / mass solution

parts per billion (ppb)

mass solutex^9 / mass solution

Electrolytes

Substances that—when dissolved—undergo either a physical or chemical change

• yields ions in solution

Strong Electrolytes

The physical/chemical process that generates the ions is essentially 100% efficient

• all dissolved compounds yield ions

Weak electrolytes

Only a relatively small fraction of the dissolved substance undergoes the ion-producing process

Non-electrolytes

Substances that do not yield ions when dissolved

Conductivity

To conduct electricity, a substance must contain freely mobile, charged species

• The brighter the bulb/electrical reactivity, the higher conductivity

Ion-dipole Attraction

The electrolyte attraction between an ion and a molecule with a dipole

• The more dissociation, the more ion formation —> STRONG electrolyte :)

Dipole

The separation of positive and negative electrical charges within a molecule, creating a "two-poled" system

Dissociation

The process by which a compound breaks into smaller components such as ions, atoms, or radicals

• often a reversible manner

• EX: H2O and KCl

Molecules in Dissociation

• Anions attract the positive charge of the dipole

• Cations attract the negative charge of the dipole