Inorganic chemistry q Calculating average atomic mass q

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Inorganic chemistry q Calculating average atomic mass. q Calculating involving molar mass of an

Inorganic chemistry q Calculating average atomic mass. q Calculating involving molar mass of an element and Avogadro's number. q Calculating the mass of a single atom. Assistance Lecturer Amjad Ahmed Juaa www. soran. edu. iq 1

q. Calculating average atomic mass: §atomic mass is an average atomic mass. The reason

q. Calculating average atomic mass: §atomic mass is an average atomic mass. The reason for this is that most naturally occurring elements have more than one isotope. The average atomic mass can be calculated as follows: Step (1): convert the percentage of each isotope to fractions. For example, isotopes that is (69. 09) percent abundant becomes : 69. 09/100 = 0. 6909 Step (2): multiply the mass of each isotope by its abundance and add them together: q. Average atomic mass = (fraction of isotopes A)( mass of isotope A) + ( fraction of isotope B)(mass of isotope B) +……. + (fraction of isotope Z)( mass of isotope Z) www. soran. edu. iq

Example: The element lithium has two isotopes that occur in nature: ( Percent abundance

Example: The element lithium has two isotopes that occur in nature: ( Percent abundance and ( ) with (7. 5) ) with (92. 5) percent abundance. The atomic mass of ( ) is (6. 01513)(amu) and that of ( average atomic mass of lithium. ) is ( 7. 01601)(amu). Calculate the Solution: Step(1): convert the percentage of each isotope to fraction: =7. 5 / 100 = 0. 075 = 92. 5 / 100 = 0. 925 www. soran. edu. iq 3

7 ﺹ 08: 46 25/07/42 Step (2): multiply the mass of each isotope by

7 ﺹ 08: 46 25/07/42 Step (2): multiply the mass of each isotope by its abundance and add them together: Average atomic mass = (0. 075)(6. 01513) + (0. 925)(7. 01601) = 6. 94. q. Calculating involving molar mass of an element and Avogadro's number: Converting between moles of atoms and mass of atoms: vfactor-label methods v Unit conversion can seem daunting. vmaking sure that the appropriate units cancel, your effort will be rewarded. Step(1): make out a strategy to proceed from initial units to final units based on available conversion factors. Step(2): use the following method to ensure that you obtain the desired unit. www. soran. edu. iq

Given unit x [ ] = desired unit. v. To convert between moles and

Given unit x [ ] = desired unit. v. To convert between moles and mass, you need to use the molar mass of the element as a conversion factor. qgoing in the direction: www. soran. edu. iq

Example: How many grams are there in (0. 130 mol ) of Cu ?

Example: How many grams are there in (0. 130 mol ) of Cu ? Solution: üYou should come up with following strategy: Moles → grams Step(2): ? g Cu = 0. 130 mol Cu x www. soran. edu. iq = 8. 26 g Cu.

q. Calculating the mass of a single atom: q. To calculate the mass of

q. Calculating the mass of a single atom: q. To calculate the mass of a single atom, you must use Avogadro's number. The conversion factor is: Example: Copper is a minor component of pennies minted since 1981, and is also used in electrical cables, calculate the mass ( in gram) of a single Cu atom. Solution: Step(1): one conversion factor needed is given above. Another necessary conversion factor is the molar mass of Cu. www. soran. edu. iq

q. You should come up with the following strategy: = 1. 055 x 10

q. You should come up with the following strategy: = 1. 055 x 10 -22 g/Cu atom. www. soran. edu. iq