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Have you ever tried counting the number of rice particles in your bowl?

Have you ever tried counting the number of rice particles in your bowl?. Relative Masses of Atoms and Molecules. Masses of Particles in Chemistry. the mass of a hydrogen atom is 0.000 000 000 000 000 000 000 0014g very small values and very inconvenient to write

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Have you ever tried counting the number of rice particles in your bowl?

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  1. Have you ever tried counting the number of rice particles in your bowl?

  2. Relative Masses of Atoms and Molecules

  3. Masses of Particles in Chemistry • the mass of a hydrogen atom is 0.000 000 000 000 000 000 000 0014g • very small values and very inconvenient to write • so, scientists do not use these actual masses in their calculation

  4. Relative Masses • scientists overcome this by comparing the masses of atoms with the mass of a carbon-12 atom • it is a ratio and has no unit

  5. Relative Atomic Mass The relative atomic mass (Ar) of an element is the average mass of one atom of the element when compared with of the mass of an atom of carbon-12. NO UNITS!

  6. Relative Molecular Mass • many elements and compounds exist as molecules • the mass of a molecule is found by adding the relative atomic masses of all atoms in the molecule • this mass is known as the relative molecular mass (Mr)

  7. Relative Molecular Mass The relative molecular mass (Mr) of a molecule is the average mass of one molecule of the substance when compared with of the mass of an atom of carbon-12. NO UNITS!

  8. Relative Formula Mass ionic compounds consist of ions, not molecules instead of relative molecular mass, we use the term relative formula mass the relative formula mass of an ionic compound is found by adding the relative atomic masses of all the atoms in the formula

  9. Let’s try! TB P137 Q2 Calculate the relative molecular/formula masses of the following substances. • H2O • NH3 • O2 • CaCO3 • H2SO4 • Cu(NO3)2 • (NH4)2SO4 • CuSO4.5H2O

  10. Percentage Composition • the percentage composition of an element in a compound can be calculated from: • the formula, and • the relative atomic masses of its elements • percentage of an element in a compound = number of atoms of the element in the formula x Ar of the element x 100% Mr of the compound

  11. Calculating the mass of an element in a compound number of atoms of the element in the formula Ar of the element x x mass of the sample Mr of the compound mass of an element in a compound =

  12. Calculating the mass of water in a compound number of water molecules in the formula x Mr of H2O x mass of the sample Mr of the compound hydrated compounds are compounds that contain water (“water of crystallisation”) crystals are dry because water is part of the crystal structure mass of water in a compound =

  13. Let’s try! TB P140 Q2 Calculate the percentage of calcium and oxygen in calcium carbonate, CaCO3, and the percentage of oxygen in CuSO4.5H2O

  14. Let’s try! TB P140 Q3 Calculate the mass of calcium in 25 g of calcium carbonate, CaCO3, and chlorine in 27 g of copper(II) chloride, CuCl2

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