Unit 3 - Composition of Substances and Solutions

Aqueous Solution

A solution where water is the solvent example) Saltwater (NaCl dissolved in water)

Avogadro’s Number (NA)

Number of particles in 1 mole of a substance, equal to 6.022 × 10²³

example) 1 mole of oxygen molecules has 6.022 × 10²³ O₂ molecules

Concentrated

A solution with a relatively large amount of solute

example) Strong coffee has a concentrated amount of caffeine

Concentration

The measured amount of solute compared to solvent in a solution

example) 1 M NaCl solution has 1 mole of NaCl in 1 L of water

Dilute

A solution with a relatively small amount of solute

example) Weak lemonade with little sugar

Dilution

Process of adding more solvent to lower solute concentration

example) Adding water to orange juice makes it less concentrated

Dissolved

When a solute spreads out evenly in a solvent

example) Sugar dissolving in tea

Empirical Formula Mass

The total average mass of atoms in the simplest formula of a compound

example) CH₂O (glucose’s empirical formula) has a mass of about 30 g/mol

Formula Mass

Sum of the average atomic masses of all atoms in a chemical formula

example) H₂O has a formula mass of about 18 amu

Mass Percentage

The mass of solute divided by total solution mass × 100

example)

Mass-Volume Percent

Solute mass divided by solution volume × 100

example) 10 g sugar in 100 mL solution = 10% (m/v)

Molar Mass

The mass in grams of 1 mole of a substance

example) 1 mole of H₂O = 18 g

Molarity (M)

Concentration unit, moles of solute per liter of solution

example) 0.5 M NaOH has 0.5 moles of NaOH in 1 L of solution

Mole

Amount of substance with 6.022 × 10²³ particles

example) 1 mole of carbon atoms = 6.022 × 10²³ atoms

Parts per Billion (ppb)

Solute-to-solution mass ratio × 10⁹

example) 1 µg solute in 1 L solution = 1 ppb

Parts per Million (ppm)

Solute-to-solution mass ratio × 10⁶

example) 1 mg solute in 1 L solution = 1 ppm

Percent Composition

Percent by mass of each element in a compound

example) H₂O is 11.2% H and 88.8% O

Solute

The part of a solution present in the smaller amount

example) Salt in saltwater

Solvent

The part of a solution present in the larger amount

example) Water in saltwater

Volume Percentage

Solute volume divided by solution volume × 100

example) 40 mL ethanol in 100 mL solution = 40% (v/v)