Molar Mass

Before we begin to find the solution to your question, let's clarify the formula for the two ionic compounds given. First, some simple generalizations:

• For your two problems, are binary ionic compounds; if one element is a metal and the other a nonmetal; the (binary) compound is made up of ions

• An ion is an atom that has gained or lost electrons

  • An ion that is gained an electron(s) is called an ANION
    ( nonmetals), negatively
    charged

  • An ion that has lost an electron(s) is called a CATION
    (metals), positively charged

  • Be careful to remember that some of the B-group elements (transition metals) can form two different ion charges

• The Molar
  Mass of a substance is the mass of 1 mole (mol) of that substance.

• The Molar Mass is expressed in the unit: grams per mole (g/mol)

• The Molar Mass in grams per mol is numerically equally to the formula mass in atomic units

Therefore, for to find the molar mass of the two ionic compounds
You submitted a) PbO2

1. First identify that this is an ionic compound

   1. Lead (Pb) is a metal, therefore it is the cation, and it is positively charges

   2. Oxygen (O) is a gas, a nonmetal, therefore it is the anion, and is negatively charged

2. Make sure the formula for the ionic compounds is written correctly such that the ionic compound overall net charge is 0 (no net charge).

   1. Lead is a B-group metal. It can form two types of cations Pb2+ or Pb4+.
       

      1. In this case, since the name of the compound is not given, then find the charge of your anion: Oxygen (O)

   2. The Oxygen ion is O2-.

   3. When you combine the Pb 4+ and O2- do their charges equal 0…? Yes! [+2 + (2 * -2)] = 0. Now you know you have a correct balanced ionic compound. The name of this would be either Plumbic
      Oxide or Lead (IV)
      Oxide.

   4. Using your balanced ionic compound. Find the formula mass of PbO2.

   Remember the Molar Mass (g/mol) is equal numerically to the formula mass Until you get comfortable use this chart to help you keep yourself in order when you are finding the formula mass

   For PbO2:

Write the correct balanced formula: PbO2

1. 1. List Every elements that makes up the formula
      Pb
      O

   2. Next list how many atoms of each element are in the formula followed by a multiplication sign
      Pb: 1 *
      O: 1 *

   3. Write down the atomic unit for each element (listed on your periodic table) by the multiplication sign.
      Pb: 1* 207.2
      O: 2* 32.00

   4. Solve each multiplication expression
      Pb: 1* 207.2 = 207.2
      O: 2*16.00 = 32.00
       

   5. Find the sum of each multiplication:
      
       

This is your formula mass is 239.2 amu.
The Molar Mass in grams per mol is numerically equally (In this case, for PbO: the numeric value is 239.2) to the molecular mass or the formula mass in atomic mass in atomic units
The Molar Mass for Lead (IV) Oxide is 239.2 g/mol.
 
B. The second, CaF is also an ionic compound.

• Follow the same steps as you did for problem A.

• Noticed that this is NOT a balanced ionic compound

  When you combine 1 Calcium ion, Ca 2+, and Fluorine ion, F-1, the overall net charge [+2 + (-1)] = +1. In order to have Overall net charge of the 0, you must have 2 Fluorine ions, F-1.

• So the correct balanced ionic compound Calcium Fluoride is CaF2

• Find CaF2formula mass, using the steps shown above.

  • The formula mass for CaF2is 78.    1

The Molar Mass for Calcium Fluoride, CaF2, is 78.1 g/mol.