Finding the Mass of a compound

Formula Mass Add up all the atomic masses in the compound’s formula Also called molecular mass if the compound is covalently bonded (forms molecules) (Remember, ionic compounds have no molecules)

Formula mass of NaCl: Look up atomic mass of Na: 23 amu Look up atomic mass of Cl: 35.3 amu

Formula mass of NaCl: Add the atomic masses together: 23 amu amu = 58.5 amu

Formula mass of K 2 CO 3 : This time you have: two K one C three O

Formula mass of K 2 CO 3 : Multiply the atomic mass by the number of atoms of that element in the formula K39.1 x 2 = 78.2 amu C12.0 x 1 = 12.0 amu O16.0 x 3 = 48.0 amu

Formula mass of K 2 CO 3 : Now add the total mass for each element in the compound K39.1 x 2 = 78.2 amu C12.0 x 1 = 12.0 amu O16.0 x 3 = 48.0 amu + ________ Formula Mass : amu

Now you try it for: Mg (NO 3 ) 2

Now you try it for: Mg (NO 3 ) 2 Element# of atoms Mg 1 N 2 O 6

Now you try it for: Mg (NO 3 ) 2 Element# of atoms Atomic mass Mg amu N amu O amu

Now you try it for: Mg (NO 3 ) 2 Mg 1 x 24.3 = 24.3 amu N 2 x 14.0 = 28.0 amu O 6 x 16.0 = 96.0 amu

Mg (NO 3 ) 2 Mg 1 x 24.3 = 24.3 amu N 2 x 14.0 = 28.0 amu O 6 x 16.0 = 96.0 amu +_______ amu

Gram Formula Mass (GFM) is the formula mass expressed in grams instead of in amu This is a much more useful and practical unit Follow the same steps as formula mass, except your answer will have units of grams, not amu

Formulas of Hydrates A HYDRATE is a an ionic compound that has water molecules attached to its crystal structure in the solid phase. These water molecules are weakly attached to the crystal, and are easily removed if the crystals are heated. Once the water is removed, the compound is called ANHYDROUS (without water).

Formulas of Hydrates Na 2 CO 3 10 H 2 O This is a sodium carbonate crystal with ten water molecules attached to every one sodium carbonate The is the symbol that “attaches” the ten water molecules to the sodium carbonate. Think of it as a “+”

Finding GFM of Hydrates Na 2 CO 3 10 H 2 O Type# of atoms atomic mass Na223 C112 O316 H 2 O = 18

Finding GFM of Hydrates Na 2 CO 3 10 H 2 O Na2 x 23 = 46 C1 x 12 = 12 O3 x 16 = 48 H 2 O 10 x 18 = g

You try it! Find the GFM of the hydrated crystal CaSO 4 2H 2 O

You try it! CaSO 4 2H 2 O Ca 40 x 1 = 40 S 32 x 1 = 32 O 16 x 4 = 64 H 2 O18 x 2 = g