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Mass Measurements In Chemistry

Mass Measurements In Chemistry. We’ve talked about the mass of atoms in terms of one or two….these masses are very small. To be practical for laboratory work , a standard of measure had to be derived so that mass quantities could be easily measured .

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Mass Measurements In Chemistry

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  1. Mass Measurements In Chemistry

  2. We’ve talked about the mass of atoms in terms of one or two….these masses are very small. To be practical for laboratory work, a standard of measure had to be derived so that mass quantities could be easily measured. To that end, scientists created a unit called the ATOMIC MASS UNIT used to measure the mass of subatomic particles.

  3. The mass of a proton or neutron was assigned a value of 1 atomic mass unit (amu). To create a system of practical measurement, scientists used the atom CARBON-12 [6 P+ and 6 No] and assigned it a mass of 12 AMU. Then they calculated the number of atoms required to make a mass of 12 grams of Carbon-12. They found it took 6.022 x 1023 atoms of C-12 to have a mass of 12 grams. In turn, each elements’ atomic mass required 6.022 x 1023 atoms to equal the same mass in grams.

  4. FOR EXAMPLE 1 atom of Oxygen 16 weighs 16 AMU . 6.022 x 1023 atoms of O-16 weighs 16 grams! This number became very important in chemistry is known as: Avagadro’s Number

  5. The quantity of matter containing Avagadro’s Number of particles, such as atoms, molecules or formula units, is known as a: Mole When working in a lab setting, the MOLE is used to determine quantities of chemicals.

  6. Mass Calculations and Chemical Formulas • Chemical Formulas represent the ELEMENTSand the NUMBER OF ATOMS of each that compose a compound. • Subscripts in formulas relate to the element immediately IN FRONT of them. • If a formula contains a PARENTHESIS followed by a subscript, the subscript multiplies ALL elements inside.

  7. EXAMPLE Ca3(PO4)2 3 atoms Ca 2 atoms P 8 atoms O

  8. Calculating Formula Weight • Formula Weight of an element of compound is the MASS in GRAMS of ONE MOLE of the element of compound. • For an element, the FW is the ATOMIC MASS from the periodic table, or for a particular ISOTOPE. • For a compound, the FW is found by counting the number of each kind of atom. • Multiply the number of atoms X the Atomic Mass Number of the element (from the PT). • Add the results and round to significant figures.

  9. Example • What is the formula weight of Calcium Carbonate? • CaCO3 1 mole Ca X 40.08 g = 40.08 g 1 mole C X 12.011 g = 12.011 g 3 moles O X 15.9994 g = + 47.9982 g = 100.0892 g = 100.09 g/mole

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