Matter and

Apuntes

• Matter and Environment 2025 NATIONAL MOLE DAY • Moles History Since atoms are extremely small and numerous in any sample of matter, scientists use a unit called the mole to count them. A mole is defined as the number of carbon atoms in exactly 12 g of pure Carbon-12. Now that we understand what a mole is, how many atoms does it contain? Is it 1,000, 3,148,382 million, or even 1 googolplex? Techniques like mass spectrometry have accurately determined that a mole contains 6.02214 × 10²³ atoms. This value is known as Avogadro's number or Avogadro's constant. • The Mole is Just a Number To utilize the mole, we need to understand concepts like molarity and molecular mass. For example, if 120 g of acetic acid (CH₃CO₂H) is dissolved in 2 L of water, we can calculate the molarity of the solution. The molar mass of acetic acid is 60 g/mol. Thus, 120 g × (1 mol/60 g) equals 2 mol. Dividing the moles by the volume gives us 2 mol/2 L = 1 mol/L = 1 M. • Concentration of a Compound in a Solution To find molarity (M), follow these steps: 1. Obtain the molar mass of the compound. 2. Divide the mass of the compound by its molar mass to find the moles. 3. Divide the moles by the...