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Understanding the Mole: Counting Atoms and Molar Mass in Chemistry

In chemistry, a mole is a fundamental unit used to quantify substances, similar to a dozen. Representing 6.02 x 10²³ particles, a mole enables the counting of atoms, ions, and molecules. For example, 1 mole of carbon equals 12 grams, while 1 mole of oxygen (O₂) weighs 32 grams. This chapter explores concepts such as molar mass, gram molecular mass, and the significance of Standard Temperature and Pressure (STP) in gas volume measurements. By mastering these concepts, we gain insight into the composition and behavior of substances in chemistry.

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Understanding the Mole: Counting Atoms and Molar Mass in Chemistry

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  1. Chapter 7 • What is a mole? • In chemistry one way to count substances is by something called a mole. • Like a dozen, a mole is a certain number of atoms and a certain mass of atoms. • A mole represents 6.02 x 10 23 particles of a substance. • Just like a dozen = 12 of something. • A mole of something contains 6.02 x 10 23 atoms, ions, particles or molecules or whatever. This is referred to as Avagadro’s number.

  2. What is a mole • Movie

  3. A mole of anything is a huge number of things. 602 with 21 zeroes after it. • 1 mole of a substance = atomic mass of an element in grams. • a mole of carbon atoms = 12 grams of carbon • a mole of oxygen atoms = 16 grams of oxygen

  4. However oxygen doesn’t run around as O it is diatomic remember. O2. • 1 mole of O2 = 2(16) grams = 6.02 x 10 23 molecules of O2 = 2(6.02 x 10 23) atoms of O

  5. What would the mass of 1 mole of the following be? • Carbon dioxide • Bromine • hydrogen • SO3

  6. What would the mass of 1 mole of the following be? • Nitrogen •  Sodium hydroxide • Aluminum sulfate • Barium nitrate

  7. What we just found is also called the gram molecular mass for molecular compounds and the gram formula mass for ionic compounds. • All the terms for mass we have been using can be combined to be called molar mass.

  8. What is the mass in grams of 1.72 mole of calcium chloride? • How many moles is 24.6 g of water?

  9. Volumes of gases change with temperature and pressure. So when we talk about the volume of a gas we talk about it at Standard Temperature and Pressure. STP • Standard Temperature = 0 C or 273 K • Standard Pressure = 101.3 kpascal or 1 atmosphere (atm) • 1 mole of gas at STP = 22.4 liters = 6.02 x 10 23 particles

  10. Since density is measured in mass /volume we can use density to find the mass of a substance.

  11. % Composition and Chemical formulas • Knowing the relative amounts of the components of a mixture or compound is often useful or important. • The relative amount of each element in a compound are expressed as % composition. • % of an element = # of grams of the element/ mass of compound X 100

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